By JULIE PACE, The Associated Press

LOS ANGELES (AP) -- President Barack Obama basked in the support of his gay and lesbian backers Wednesday night, revving up an enthusiastic crowd with a pledge to block any attempt to roll back rights that gay Americans have gained under his administration.

With his public embrace of same-sex marriage just weeks old, a standing ovation with sustained applause greeted the president at a 600-person campaign fundraiser in Los Angeles for gay and lesbian supporters.

The president, nearing the end of a lengthy day of West Coast fundraising, appeared to feed off the energy of a crowd that included a handful of celebrities, including comedian Ellen DeGeneres and the singer Cher.

Making the case for his re-election, Obama said he would refuse to allow anyone to attempt to reinstate the military's ban on openly gay service members, a measure the president had fought to repeal.

"That's not something I will tolerate," he said.

Some Republicans have said they would back the reinstatement of the "don't ask, don't tell" law. Mitt Romney, Obama's Republican rival in the presidential race, is not among them.

Obama ticked through what he called his presidential "to-do" list, saying "we've gotten some stuff done over the last three-and-a-half years." After launching into a passionate defense of his contested health care overhaul, he referred back to the to-do list. "Check," he said.

The president expected to raise more than $5 million for his re-election campaign and the Democratic Party during fundraisers in San Francisco and Los Angeles on Wednesday and Thursday.

Earlier Wednesday during an event in San Francisco, Obama conceded that people around the country are wondering if he can keep his promise to build an economy designed for the long term. But he blasted opponents as offering nothing more than finger-pointing as a platform.

Obama told donors at the $5,000 per person fundraiser that "the other side" doesn't have any new ideas.

"And because they don't have any new ideas, what they will do is spend 500, 700, a billion dollars in negative ads and their simple message will be: This is someone else's fault and that's enough reason for you to vote for us," he said.

"And," he added, "if we don't answer them, that can work."

In "Virginia or Iowa or North Carolina or California, all across the country," Obama said, "there are a lot of folks who are still wondering - are we going to be able to fully deliver on that promise of a country that is thriving and has an economy that is built to last?"

Obama offered no new prescriptions for how he would answer Americans' economic questions. He said he's pushing a number of bills in Congress aimed at boosting jobs and growth but has gotten little help from Republican lawmakers.

The president was introduced by Hall of Fame baseball player Willie Mays, a former outfielder for the New York Giants and San Francisco Giants.

Following his fundraising drive in California, Obama was heading to Nevada on Thursday for a speech at the University of Nevada, Las Vegas. The president planned to announce new steps to help college students repay their loans and his efforts to jumpstart the economy.

Below, pictures of the First Family with celebrities:
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  • George Clooney & President Obama

    Actor George Clooney leaves after he spoke to the media March 15, 2012 at the White House in Washington, DC. Clooney had meeting with President Barack Obama to discuss the current situations in Darfur, Sudan. (Photo by Alex Wong/Getty Images)

  • President Obama & Tyler Perry

    Actor and director Tyler Perry hugs US President Barack Obama during a campaign event at Tyler Perry Studios March 16, 2012 in Atlanta, Georgia. President Obama is spending the day traveling to Chicago, Illinois and Atlanta, Georgia to attend private and public campaign events. (Photo by BRENDAN SMIALOWSKI/AFP/Getty Images)

  • The Obamas & Oprah Winfrey

    US President Barack Obama and First Lady Michelle Obama chat with talk show host Oprah Winfrey during a taping of the Oprah Winfrey show April 27, 2011 at Harpo Studios in Chicago. (Photo by MANDEL NGAN/AFP/Getty Images)

  • President Obama & Magic Johnson

    In this handout image provided by the U.S. Navy, President Barack Obama is greeted on the court by NBA Hall of Fame basketball player Earvin 'Magic' Johnson and Michigan State University assistant coach Mike Garland. (Photo by Mass Communication Specialist 2nd Class James R. Evans/U.S. Navy via Getty Images)

  • Willow Smith Performs At The White House

    Willow Smith, daughter of Will Smith and Jada Pinkett Smitt, performs during the White House Easter Egg Roll on the South Lawn of the White House on April 25, 2011 in Washington, DC. (Photo by Roger L. Wollenberg-Pool/Getty Images)

  • Antonio Banderas & President Obama

    Antonio Banderas and his wife Melanie Griffith hosted a fundraising event for President Obama in October 2011. (Photo by Sean Gallup/Getty Images)

  • Tom Hanks Narrates Pro-Obama Film

    This 17-minute film released by President Obama's re-election campaign was directed by Davis Guggenheim (director of "An Inconvenient Truth") and narrated by actor Tom Hanks.

  • Gov. Mitt Romney & Jeff Foxworthy

    Republican presidential candidate, former Massachusetts Gov. Mitt Romney makes a campaign appearance with comedian Jeff Foxworthy at the Whistle Stop cafe March 12, 2012 in Mobile, Alabama. (Photo by Win McNamee/Getty Images)

  • Gov. Mitt Romney & Kid Rock

    Republican presidential candidate and former Massachusetts Gov. Mitt Romney greets musician Kid Rock during a campaign rally at the Royal Oak Theatre on February 27, 2012 in Royal Oak, Michigan. (Photo by Justin Sullivan/Getty Images)

  • David Mustaine & Rick Santorum

    David Mustaine of Megadeth expressed support for Rick Santorum in a February <a href="http://www.musicradar.com/news/live/interview-megadeths-dave-mustaine-talks-guitar-politics-and-todays-music-529703" target="_hplink">interview with Music Radar</a>.

  • Kelly Clarkson & Ron Paul

    Kelly Clarkson tweeted about her love for Ron Paul in late 2011, but dialed it back slightly after a backlash accused her of supporting Paul's racist and homophobic publications, <a href="http://www.foxnews.com/entertainment/2012/03/09/kelly-clarkson-never-endorsed-ron-paul/" target="_hplink">reports Fox News</a>. (Photo by ROBYN BECK/AFP/Getty Images)

  • Snoop Dogg & Ron Paul

    In December 2011, Snoop Dogg posted a picture of Ron Paul on his Facebook page with the caption "Smoke Weed Every Day," <a href="http://www.reuters.com/article/2012/01/31/us-snoopdogg-ronpaul-idUSTRE80U04220120131" target="_hplink">reports Reuters</a>. (Photo by Ethan Miller/Getty Images for Keep Memory Alive)

  • Oliver Stone & Ron Paul

    In January, Oliver Stone told <a href="http://www.rockcellarmagazine.com/2012/01/12/director-oliver-stone-on-history-and-america-jim-morrison-ron-paul/" target="_hplink">Rock Cellar Magazine</a> that he would vote for Ron Paul over Barack Obama if Paul was named the GOP nominee because "he's the only one of anybody who's saying anything intelligent about the future of the world." (Photo by Stephen Morton/Getty Images)