The pop singer showed up at the Sandberg affair in Atherton, Calif., attired in super-high heels and a floor-length, sleeveless black dress with her blond hair in a bouffant up-do accented by a black hairpiece and black veil. She sat at a center table under the white party tent set up in the home's back yard.
Obama, who spoke for several minutes, didn't mention Gaga's presence, though it was possible they had met inside the house prior to the dinner.
The Democratic president, who is building up his campaign war chest for his 2012 re-election bid, told the supporters he believes in an America that is diverse, tolerant and generous.
"But we're going to have to fight for that vision," he said. "We've made enormous progress but we've got a lot more work to do."
Those in attendance paid $35,800 per person or couple.
At an earlier fundraiser in San Jose, Calif., Obama went after the Republican presidential candidates, including Texas Gov. Rick Perry -- though he didn't utter his name -- saying next year's election will be "a contest of values."
"Some of you here may be folks who actually used to be Republicans but are puzzled by what's happened to that party, are puzzled by what's happening to that party," Obama said. "I mean, has anybody been watching the debates lately? You've got a governor whose state is on fire denying climate change. It's true. You've got audiences cheering at the prospect of somebody dying because they don't have healthcare and booing a service member in Iraq because they're gay.
"That's not reflective of who we are. This is a choice about the fundamental direction of our country; 2008 was an important direction, 2012 is a more important election."
Earlier in the day, Obama attended two fundraisers in the Seattle area.