By Ronnie Cohen

SAN FRANCISCO, Sept 28 (Reuters) - The Obama administration has directed immigration officials to recognize same-sex partners as family members in deportation cases, House Minority Leader Nancy Pelosi said on Friday.

Homeland Security Secretary Janet Napolitano told Pelosi in a letter that she had ordered U.S. Immigration and Customs Enforcement to notify its field offices "that the interpretation of the phrase 'family relationships' includes long-term, same-sex partners."

Pelosi welcomed the federal recognition of gay and lesbian couples. At the same time, she called for more to be done to protect undocumented immigrants in long-term relationships with American citizens.

Napolitano's directive "will provide a measure of clarity and confidence to families dealing with separation in immigration cases," Pelosi said in a written statement. "Our nation is served when loving families are kept together."

But she added: "We need to ... relegate DOMA to the dustbin of history." The 1996 Defense of Marriage Act bars the federal government from extending federal benefits, such as Social Security, to married gay and lesbian couples.

DOMA restricts the Obama administration from outright ordering that gay and lesbian couples be treated the same as heterosexual couples.

Last year, Attorney General Eric Holder and President Barack Obama called DOMA unconstitutional and said they would no longer defend the measure in court. In response, the Republican-controlled U.S. House of Representatives stepped in to fund an effort to try to uphold the law.

The U.S. Supreme Court is expected to decide next month whether it will review a number of cases questioning the constitutionality of DOMA.

Meanwhile, married couples like Brian Willingham, 38, and Alfonso Garcia, 35, of Orinda, California, have been fighting for the right to be considered related in the eyes of immigration authorities. After a traffic stop, officials began deportation proceedings against Garcia, who came to the United States from Mexico when he was 14.

"We're definitely happy that the Obama administration took this good first step," Willingham told Reuters Friday. "But it's just a Band-Aid. It helps us because we are faced with deportation. But it leaves thousands of couples in exile."

Immigration officials last year said they would consider same-sex partnerships as family relations in deciding whether to deport undocumented immigrants.

But 83 members of Congress led by Pelosi and Jerrold Nadler of New York criticized the government for unevenly applying the directive, and they pressed for written guidelines.

"This is a huge step forward," said Rachel B. Tiven, executive director of Immigration Equality, a national gay-rights group. "Until now, LGBT families and their lawyers had nothing to rely on but an oral promise. The administration's written guidance will help families facing separation and the field officers who are reviewing their cases." (Reporting By Ronnie Cohen; Editing by Mary Wisniewski and Todd Eastham)