The black-tie dinner, informally billed as the "nerd prom," is the biggest social event of the year for Washington media and gives presidents a chance to show a lighter side.

"I'm not going to attack any of the Republican candidates. Take Mitt Romney; he and I actually have a lot in common," the president said, telling the crowd of Hollywood celebrities and Washington power players that both men trailed their wives in national opinion polls.

Obama, who faces re-election in November, is expected to be matched against Romney, a multimillionaire and former Massachusetts governor.

He joked that the luxurious ballroom in the Washington Hilton hotel where the dinner was held was "what Mitt Romney calls a fixer-upper," a dig at Romney's sometimes clumsy references to his wealth.

Obama said he had expected a tough campaign but that one video had gone too far. A fake political attack ad rolled with a news clip of Romney defending himself against criticism for strapping the family dog, Seamus, in a crate on the top of the car during a family trip in 1983.

The clip showed images of the Obama family dog Bo, apparently miserable at being held captive by "European style dog socialism." A deep voice intoned: "American dogs can't afford four more years of Obama. To them, that's 28 years."

Obama also took a shot at former Speaker of the House Newt Gingrich, who has announced he would quit the Republican primary race. "Newt, there's still time man," he said to Gingrich, who was in the audience with his wife, Callista.

SECRET SERVICE 'CURFEW'

In a shot at the legislative branch of the U.S. government, Obama quipped: "Congress and I have certainly had our differences. Yet, I've tried to be civil, to not take any cheap shots and that's why I want to especially thank all the members who took a break from their exhausting schedule of not passing any laws to be here tonight. Let's give them a big round of applause."

Obama ended his speech with a reference to a recent scandal over Secret Service staffers consorting with prostitutes during a presidential trip to Colombia. "I had a lot more material prepared, but I have to get the Secret Service home in time for their new curfew."

Last year, the president told jokes at the expense of U.S. real estate mogul Donald Trump, mocking his possible presidential ambitions. That dinner came on the eve of the announcement that U.S. Navy SEALs had killed al Qaeda leader Osama bin Laden.

Late-night TV comedian Jimmy Kimmel, who was the featured entertainer, wondered "Who'll it be this year?" and joked, "You know there's a term for guys like President Obama, um, probably not two terms."

Kimmel continued the dog-themed jokes with a jab at the president, who shocked some Americans with the revelation that he ate dog meat as a child in Indonesia.

"When you go to a dog park, is this the same as when we look at a tank full of lobsters?" Kimmel asked.

Among the guests at the dinner, sponsored by the White House Correspondents Association, was a large contingent of entertainment celebrities invited by media organizations.

Among them were director Steven Spielberg, actors George Clooney, Sigourney Weaver, Claire Danes and Kevin Spacey, Eva Longoria, Goldie Hawn and Reese Witherspoon, and singer John Legend.

Seated at the same table were reality television star Kim Kardashian and actress Lindsay Lohan.

(Reporting By Lily Kuo; Editing by Eric Walsh and Todd Eastham)

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