Speaking to the Hollywood audience, Obama said his public endorsement of same-sex marriage was "a logical extension of what America is supposed to be."
"Are we a country that includes everybody and gives everybody a shot and treats everybody fairly and is that going to make us stronger?" Are we welcoming to immigrants? Are we welcoming to people who aren't like us? Does that make us stronger? I believe it does," he said.
The guest list for the dinner at Clooney's home included Robert Downey Jr., Tobey Maguire, Barbra Streisand, director-producer J.J. Abrams, and DreamWorks Animation Chief Executive Jeffrey Katzenberg, one of the event's organizers, the Los Angeles Times reported.
The event was expected to raise an estimated $15 million. Tickets sold for $40,000 but two-thirds of the total proceeds were expected to come from the public, through an online contest offering a chance to rub elbows with the stars, the newspaper said.
Katzenberg spoke to the crowd, saying, "Once again the entertainment industry has stepped forward in a very big way."
As the president's motorcade traveled from Bob Hope Airport in Burbank to Clooney's home in Studio City -- where helicopters hovered overhead and traffic patterns were disrupted for miles around -- fans and supporters of the president held up signs saying "Obama 2012"; "We (heart) U Obama"; "Our gay family says thanks Mr. President"; and "Will trade Lakers for Bulls if you stop!"
Speaking at a fundraiser in Seattle Thursday afternoon, Obama told supporters "your country needs your help."
"You did not join the campaign because of me," he said, speaking of the 2008 campaign. "You came together -- we came together -- because of a shared vision. We came together to reclaim that basic bargain that built the largest middle class and the most prosperous nation on Earth.
"We came together because we believed that in America, your success shouldn't be determined by the circumstances of your birth," the president said.
Obama said his administration is making progress but "we've got more work to do."
"But here's what else we know: That the last thing we can afford is a return to the policies that got us here in the first place," he said.
"What Governor Romney does not seem to get is that a healthy economy doesn't just mean maximizing your own profits through massive layoffs or busting unions," the president said.
Obama said government "shouldn't try to solve all our problems."
"And Democrats, we have to remember some things," he said. "Not every regulation is smart. Not every tax dollar is spent wisely. Not every person can be helped who refuses to help themselves. We believe in individual responsibility."