By Ellen Wulfhorst

July 9 (Reuters) - Activists will focus efforts to legalize same-sex marriage in four U.S. states this year and next, hoping to capitalize on political momentum following U.S. Supreme Court victories for gay rights, the Freedom to Marry advocacy group said on Tuesday.

The group is targeting Hawaii, Illinois and New Jersey, where legislative measures to legalize same-sex marriage have failed, and Oregon, where there is a drive to put a gay marriage initiative on the ballot in November.

While the Supreme Court justices stopped short of declaring a nationwide right to same-sex marriage, it ruled that the federal government must recognize same-sex marriages in states where it is legal.

"It's obviously a very exciting time in our movement and in our campaign," said Evan Wolfson, founder and head of Freedom to Marry. "We have tremendous momentum from the wins that we secured at the ballot last year, the three states that we've already won this year and of course the Supreme Court rulings."

Thirteen U.S. states and the District of Columbia recognize gay marriage. Among them, Delaware, Minnesota and Rhode Island legalized gay marriage this year.

Opponents of same-sex marriage called the Freedom to Marry's four-state strategy overly optimistic.

"They're hugely overplaying their hand," said Thomas Peters, a spokesman for the National Organization for Marriage, which opposes gay marriage.

"These are states where gay marriage advocates have been saying for months, if not years, that gay marriage is inevitable and they've made no progress."

In Illinois, a bill to recognize same-sex marriage stalled in the state legislature this year but could be revived when lawmakers return in the fall.

New Jersey is shaping up as a battleground as Democrat lawmakers seek enough votes to overturn Republican Governor Chris Christie's veto of same-sex marriage legislation last year.

Freedom to Marry also said it is targeting at least six more states to pass same-sex marriage in 2015 and 2016 that may include Arizona, Colorado, Michigan, Nevada, New Mexico, North Carolina, Ohio, Pennsylvania and Virginia. (Reporting by Ellen Wulfhorst in New York; Editing by Lisa Shumaker)

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  • WASHINGTON, DC - JUNE 26: Married couple Michael Knaapen (L) amd John Becker (2nd L) react after hearing the U.S. Supreme Court ruled that the Defense of Marriage Act (DOMA) is unconstitutional at the Supreme Court, June 26, 2013 in Washington, DC. The high court ruled to strike down DOMA and determined the California's proposition 8 ban on same-sex marriage was not properly before them, declining to overturn the lower court's striking down of the law. (Photo by Mark Wilson/Getty Images)

  • WASHINGTON, DC - JUNE 26: Married couple Michael Knaapen (L) amd John Becker (2nd L) kiss after hearing the U.S. Supreme Court ruled that the Defense of Marriage Act (DOMA) is unconstitutional at the Supreme Court, June 26, 2013 in Washington, DC. The high court ruled to strike down DOMA and determined the California's proposition 8 ban on same-sex marriage was not properly before them, declining to overturn the lower court's striking down of the law. (Photo by Mark Wilson/Getty Images)

  • Michael Knaapen, left, and his husband John Becker, right, embrace outside the Supreme Court in Washington, Wednesday, June 26, 2013, after the court cleared the way for same-sex marriage in California by holding that defenders of California's gay marriage ban did not have the right to appeal lower court rulings striking down the ban. (AP Photo/Charles Dharapak)

  • NEW YORK, NY - JUNE 26: Richelle Spanover (2nd R) wipes her eye after after the Supreme Court ruled key portions of the Defense of Marriage Act (DOMA) unconstitutional, at the Stonewall Inn on June 26, 2013 in the West Village neighborhood of New York City. The Stonewall Inn became historically important in the Lesbian-Gay-Bigender-Transgender community after playing a key role during the Gay-rights movement of the 1960s and 1970s. The high court ruled to strike down DOMA and determined the California's proposition 8 ban on same-sex marriage was not properly before them, declining to overturn the lower court's striking down of the law. (Photo by Andrew Burton/Getty Images)

  • NEW YORK, NY - JUNE 26: Virginia Sin (L) and Gretchen Menter smile after the Supreme Court ruled key portions of the Defense of Marriage Act (DOMA) unconstitutional, at the Stonewall Inn on June 26, 2013 in the West Village neighborhood of New York City. The Stonewall Inn became historically important in the Lesbian-Gay-Bigender-Transgender community after playing a key role during the Gay-rights movement of the 1960s and 1970s. The high court ruled to strike down DOMA and determined the California's proposition 8 ban on same-sex marriage was not properly before them, declining to overturn the lower court's striking down of the law. (Photo by Andrew Burton/Getty Images)

  • Edith Windsor, center, accompanied by her attorney Roberta Kaplan, right, is greeted by Orie Urami, left, as she arrives at the LGBT Center for a news conference, in New York, Wednesday, June 26, 2013. In a major victory for gay rights, the Supreme Court on Wednesday struck down a provision of a federal law denying federal benefits to married gay couples and cleared the way for the resumption of same-sex marriage in California. (AP Photo/Richard Drew) <em><strong>CORRECTION:</strong> This slide initially referred to Edith Windsor's attorney as Robert Kaplan. Her name is Roberta Kaplan.</em>

  • David Boies, an attorney arguing in support of gay marriage, speaks to the media after the U.S. Supreme Court overturned the Defense of Marriage Act (DOMA) and declined to rule on the California law Proposition 8 in Washington, D.C., U.S. on Wednesday, June 26, 2013. A divided U.S. Supreme Court gave a landmark victory to the gay-rights movement, striking down a federal law that denies benefits to same-sex married couples and clearing the way for weddings to resume in California. Photographer: Joshua Roberts/Bloomberg via Getty Images

  • Chris Roe (L) and Roby Chavez (R) celebrate while holding their soon-to-be adopted children as the US Supreme Court ruling is announced on June 26, 2013. The US Supreme Court struck down The Defense of Marriage Act (DOMA) today, and declared that same-sex couples who are legally married deserve equal rights to the benefits under federal law that go to all other married couples. In another ruling, the Supreme Court cleared the way for same-sex marriages to resume in California as the justices, in a prcedural ruling, turned away the defenders of Proposition 8. AFP PHOTO/Josh Edelson (Photo credit should read Josh Edelson/AFP/Getty Images)

  • Edith Windsor arrives at the LGBT Center for a news conference, in New York, Wednesday, June 26, 2013. In a major victory for gay rights, the Supreme Court on Wednesday struck down a provision of a federal law denying federal benefits to married gay couples and cleared the way for the resumption of same-sex marriage in California. (AP Photo/Richard Drew)

  • Edith Windsor reacts during a news conference at the LGBT Center, in New York, Wednesday, June 26, 2013. In a major victory for gay rights, the Supreme Court on Wednesday struck down a provision of a federal law denying federal benefits to married gay couples and cleared the way for the resumption of same-sex marriage in California. (AP Photo/Richard Drew)

  • Kris Perry, second from right, kisses her partner Sandy Stier outside the Supreme Court in Washington, Wednesday, June 26, 2013, after the court cleared the way for the resumption of same-sex marriage in their home state of California. From left are, plaintiffs Jeff Zarrillo, and his partner Paul Katami, attorney David Boies, plaintiffs Sandy Stier and Kris Perry, and attorney Ted Boutrous. (AP Photo/J. Scott Applewhite)

  • John Lewis, left, and Stuart Gaffney embrace outside San Francisco's City Hall shortly before the U.S. Supreme Court ruling cleared the way for same-sex marriage in California on Wednesday, June 26, 2013. The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits. The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. (AP Photo/Noah Berger)

  • Sandy Stier, center, and her partner Kris Perry, right, plaintiffs in Hollingsworth v. Perry, the California Proposition 8 case, meets with reporters outside the Supreme Court in Washington, Wednesday, June 26, 2013, after the court's 5-4 decision that cleared the way for the resumption of same-sex marriage in their home state of California. Gesturing at far left is fellow plaintiff Jeff Zarrillo. (AP Photo/J. Scott Applewhite)

  • WASHINGTON, DC - JUNE 26: American University students Sharon Burk (L) and Mollie Wagoner (R) embrace after hearing that the U.S. Supreme Court ruled that the Defense of Marriage Act (DOMA) is unconstitutional at the Supreme Court, June 26, 2013 in Washington, DC. The high court ruled to strike down DOMA and determined the California's proposition 8 ban on same-sex marriage was not properly before them, declining to overturn the lower court's striking down of the law. (Photo by Mark Wilson/Getty Images)

  • John Lewis, left, and his partner Stuart Gaffney embrace as they react next to Andrea Shorter after the Supreme Court decision at the office of San Francisco Mayor Ed Lee at City Hall in San Francisco, Wednesday, June 26, 2013. The Supreme Court on Wednesday struck down a provision of a U.S. law denying federal benefits to married gay couples and cleared the way for the resumption of same-sex marriage in the state of California. The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits. The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. (AP Photo/Jeff Chiu)

  • SAN FRANCISCO, CA - JUNE 26: Same-sex couple Jewelle Gomez (R) and Diane Sabin react upon hearing the U.S. Supreme Court's rulings on gay marriage in City Hall June 26, 2013 in San Francisco, California. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Justin Sullivan/Getty Images)

  • Gay rights activist Bryce Romero, who works for the Human Rights Campaign, offers an enthusiastic high-five to visitors getting in line to enter the Supreme Court on a day when justices are expected to hand down major rulings on two gay marriage cases that could impact same-sex couples across the country, in Washington, Wednesday, June 26, 2013. (AP Photo/J. Scott Applewhite)

  • Gay rights activist Bryce Romero, who works for the Human Rights Campaign, offers an enthusiastic high-five to visitors getting in line to enter the Supreme Court on a day when justices are expected to hand down major rulings on two gay marriage cases that could impact same-sex couples across the country, in Washington, Wednesday, June 26, 2013. (AP Photo/J. Scott Applewhite)

  • WASHINGTON, DC - JUNE 26: Attorney David Boise (C) speaks while flanked by plantiff couples Paul Katami, (L), Jeff Zarillo (2nd L), Sandy Steier (2nd R) and Kris Perry (R) after the U.S. Supreme Court ruled that part of the Defense of Marriage Act (DOMA) is unconstitutional at the Supreme Court, June 26, 2013 in Washington, DC. The high court ruled to strike down DOMA and determined the California's proposition 8 ban on same-sex marriage was not properly before them, declining to overturn the lower court's striking down of the law. (Photo by Mark Wilson/Getty Images)

  • Plaintiffs in Hollingsworth v. Perry, the California Proposition 8 case, react on steps of the Supreme Court in Washington, Wednesday, June 26, 2013, after justices cleared the way for the resumption of same-sex marriage in California. From left are, Jeff Zarrillo, and his partner Paul Katami, attorney David Boies, and Sandy Stier and her partner Kris Perry. (AP Photo/J. Scott Applewhite)

  • Michael Knaapen (L) and his husband John Becker react outside the US Supreme Court in Washington DC on June 26, 2013. The US Supreme Court on Wednesday struck down a controversial federal law that defines marriage as a union between a man and a woman, in a major victory for supporters of same-sex marriage.The Defense of Marriage Act (DOMA) had denied married gay and lesbian couples in the United States the same rights and benefits that straight couples have long taken for granted. AFP PHOTO / MLADEN ANTONOV (Photo credit should read MLADEN ANTONOV/AFP/Getty Images)

  • WASHINGTON, DC - JUNE 26: Chase Hardin hugs friend Kai Neander on the steps of the Supreme Court after favorable rulings were issued in same sex marriage cases June 26, 2013 in Washington, DC. The high court ruled to strike down DOMA and determined the California's proposition 8 ban on same-sex marriage was not properly before them, declining to overturn the lower court's striking down of the law. (Photo by Win McNamee/Getty Images)

  • WASHINGTON, DC - JUNE 26: Gay rights supporter Jay Norris, of New York City, holds a U.S. flag outside the U.S. Supreme Court building on June 26, 2013 in Washington, DC. The high court is expected to rule on the DOMA and Prop 8 gay marriage cases. (Photo by Win McNamee/Getty Images)

  • WEST HOLLYWOOD, CA - JUNE 26: Martha Acevedo, 25, celebrates the Supreme Court ruling after a watch party at Equality California, a non-profit civil rights organization that advocates for the rights of LGBT people in California, on June 26, 2013 in West Hollywood, California. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Kevork Djansezian/Getty Images)

  • Ellen Pontac, left, and her wife Shelly Bailes, celebrate in Sacramento, Calif., after the U.S. Supreme Court's ruling on gay marriage in California, Wednesday, June 26, 2013. The 5-4 decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples, like Pontac and Bailes, from receiving tax, health and pension benefits. (AP Photo/Rich Pedroncelli) will now have the same (AP Photo/Rich Pedroncelli)

  • Attendees at a watch party in Miami celebrate after the U.S. Supreme Court's ruling on gay marriage in California Wednesday, June 26, 2013. The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits. The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. (AP Photo/Wilfredo Lee)

  • Julia Tate, left, kisses her wife, Lisa McMillin, as they read results of Supreme Court decisions regarding gay rights on Wednesday, June 26, 2013, in Nashville, Tenn. The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits. The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. McMillin holds the couple's son, Luke. (AP Photo/Mark Humphrey)

  • Juan Talavera, right, kisses his partner Jeff Ronci after the announcement of the U.S. Supreme Court's ruling at a watch party in Miami, Wednesday, June 26, 2013. The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits. The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. (AP Photo/Wilfredo Lee)

  • Renata Moreira, right, and partner Lori Bilella cheer after the U.S. Supreme Court's ruling on gay marriage in California, at San Francisco's City Hall on Wednesday, June 26, 2013. The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits. The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. The couple plans to marry. (AP Photo/Noah Berger)

  • WEST HOLLYWOOD, CA - JUNE 26: Erica Ikeda (C), 26, and Jessica Parral (R), 24, react to the Supreme Court ruling at a watch party at Equality California, a non-profit civil rights organization that advocates for the rights of LGBT people in California, on June 26, 2013 in West Hollywood, California. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Kevork Djansezian/Getty Images)

  • WEST HOLLYWOOD, CA - JUNE 26: Brandon Benoit (C) hugs Martha Acevedo (L), 25, and Briana Castaneda, 23, as they celebrate the Supreme Court ruling at a watch party at Equality California, a non-profit civil rights organization that advocates for the rights of LGBT people in California, on June 26, 2013 in West Hollywood, California. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Kevork Djansezian/Getty Images)

  • WEST HOLLYWOOD, CA - JUNE 26: People celebrate in the street after the Supreme Court ruling at a watch party at Equality California, a non-profit civil rights organization that advocates for the rights of LGBT people in California, on June 26, 2013 in West Hollywood, California. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Kevork Djansezian/Getty Images)

  • SAN FRANCISCO, CA - JUNE 26: Supporters of same-sex marriage cheer as they learn results of the U.S. Supreme Court's rulings on gay marriage in City Hall June 26, 2013 in San Francisco, United States. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Justin Sullivan/Getty Images)

  • SAN FRANCISCO, CA - JUNE 26: Same-sex couple Sue Rochman (L) and Robin Romdalvik celebrate upon hearing the U.S. Supreme Court's rulings on gay marriage in City Hall June 26, 2013 in San Francisco, United States. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Justin Sullivan/Getty Images)

  • Gay rights activists reacts outside the US Supreme Court building in Washington DC on June 26, 2013, after the court ruling on California's Proposition 8, the controversial ballot initiative that defines marriage as between a man and a woman. AFP PHOTO / MLADEN ANTONOV (Photo credit should read MLADEN ANTONOV/AFP/Getty Images)

  • WEST HOLLYWOOD, CA - JUNE 26: Erica Ikeda (C), 26, and her friends react to the Supreme Court ruling at a watch party at Equality California, a non-profit civil rights organization that advocates for the rights of LGBT people in California, on June 26, 2013 in West Hollywood, California. The high court struck down the Defense of Marriage Act (DOMA) and ruled that supporters of California's ban on gay marriage, Proposition 8, could not defend it before the Supreme Court. (Photo by Kevork Djansezian/Getty Images)

  • John Lewis, left, gets a kiss from his partner Stuart Gaffney as they embrace after the Supreme Court cleared the way for same-sex marriage in California at the office of San Francisco Mayor Ed Lee at City Hall in San Francisco, Wednesday, June 26, 2013. The justices issued two 5-4 rulings in their final session of the term. One decision wiped away part of a federal anti-gay marriage law that has kept legally married same-sex couples from receiving tax, health and pension benefits. The other was a technical legal ruling that said nothing at all about same-sex marriage, but left in place a trial court's declaration that California's Proposition 8 is unconstitutional. (AP Photo/Jeff Chiu)

  • WASHINGTON, DC - JUNE 26: Plaintiff couple Sandy Stier (C) and Kris Perry (L) arrive for their Proposition 8 case before the U.S. Supreme Court on June 26, 2013 in Washington, DC. The high court is expected to rule on the DOMA and Prop 8 gay marriage cases. (Photo by Win McNamee/Getty Images)

  • WASHINGTON, DC - JUNE 26: Gay rights supporters Brian Sprague (L) and Charlie Ferrusi, from Albany, New York, hold a Human Rights flag outside U.S. Supreme Court building on June 26, 2013 in Washington, DC. The high court is expected to rule on the DOMA and Prop 8 gay marriage cases. (Photo by Win McNamee/Getty Images)

  • WASHINGTON, DC - JUNE 26: Gay rights supporter Vin Testa waves a rainbow flag outside the U.S. Supreme Court building on June 26, 2013 in Washington, DC. The high court is expected to rule on the DOMA and Prop 8 gay marriage cases. (Photo by Win McNamee/Getty Images)

  • Gay rights activists gather outside the US Supreme Court building in Washington, DC on June 26, 2013. The US Supreme Court on Wednesday struck down a controversial federal law that defines marriage as a union between a man and a woman, in a major victory for supporters of same-sex marriage.The Defense of Marriage Act (DOMA) had denied married gay and lesbian couples in the United States the same rights and benefits that straight couples have long taken for granted. AFP PHOTO / MLADEN ANTONOV (Photo credit should read MLADEN ANTONOV/AFP/Getty Images)

  • American University students Sharon Burk, left, and Molly Wagner, embrace outside the Supreme Court in Washington, Wednesday, June 26, 2013, after the court cleared the way for same-sex marriage in California by holding that defenders of California's gay marriage ban did not have the right to appeal lower court rulings striking down the ban. (AP Photo/Charles Dharapak)

  • Arriving at the Supreme Court in Washington, Wednesday, June 26, 2013, on a final day for decisions in two gay marriage cases are plaintiffs in the California Proposition 8 case, from left, Paul Katami, his partner Jeff Zarrillo, and Sandy Stier and her partner Kris Perry. (AP Photo/J. Scott Applewhite)

  • Michael Knaapen, left, and his husband John Becker, right, embrace outside the Supreme Court in Washington, Wednesday, June 26, 2013 after the court struck down a federal provision denying benefits to legally married gay couples. (AP Photo/Charles Dharapak)

  • American University students Sharon Burk, left, and Molly Wagner participate in a rally for rights for gay couples in front of the Supreme Court in Washington, Wednesday, June 26, 2013, after the court cleared the way for same-sex marriage in California by holding that defenders of California's gay marriage ban did not have the right to appeal lower court rulings striking down the ban. (AP Photo/Charles Dharapak)

  • Supporters of gay marriage embrace outside the Supreme Court in Washington, Wednesday, June 26, 2013, after the court cleared the way for same-sex marriage in California by holding that defenders of California's gay marriage ban did not have the right to appeal lower court rulings striking down the ban. (AP Photo/Charles Dharapak)

  • Sen. Richard Blumenthal (D-Conn.) spotted in the crowd during the SCOTUS decisions on June 26