* "You're hired," conservative yells at Trump
* Conservatives seek to defeat Obama next year
* Search for Republican challengers to Obama (Updates with Pawlenty's prepared remarks)
WASHINGTON, Feb 10 (Reuters) - Potential U.S. Republican presidential candidates flocked to a gathering of conservatives on Thursday to road-test a message that basically boiled down to this: Beat President Barack Obama in 2012.
Republicans have no obvious heir-apparent for 2012, leaving 11,000 conservatives at a conference to ponder a crowded field fighting for attention 21 months before the election.
Newt Gingrich, the former speaker of the House of Representatives who is flirting with a run next year, declared that Republican victories in congressional elections last year were only the start. "2010 was the appetizer, 2012 is the entree," he told the Conservative Political Action Conference.
Representative Michele Bachmann, a Tea Party champion often mentioned as a potential 2012 contender, told the group that Republicans' main goal was "making Barack Obama a one-term president."
The party is on a roll after wresting control of the House from the Democrats in November's elections and battling Obama on spending cuts.
But Obama may be hard to beat. He appears to be enjoying an improved standing with Americans by making some centrist moves after his Democrats were routed in the elections.
Celebrity real estate tycoon Donald Trump, a surprise speaker, drew the largest crowd of the day and criticized Obama's economic policies.
Nobody knows whether Trump is serious about running for president. But he came with plenty of talking points, complaining the United States needs to get tougher with China over its currency policy and with OPEC nations for high oil prices.
"If I decide to run, I will not be raising taxes," Trump said. "We will be taking hundreds of billions of dollars from other countries that are screwing us."
Trump is perhaps America's most famous businessman. He presided over the popular NBC program "The Apprentice" with the signature line "You're fired."
So perhaps it was inevitable that when he declared he would decide by June whether to become a candidate, someone yelled from the crowd, "You're hired."
The crowd also got an unexpected appearance from former Vice President Dick Cheney, who introduced former Defense Secretary Donald Rumsfeld.
The gathering came as sniping broke out between two potential candidates -- former Alaska Governor Sarah Palin and former Senator Rick Santorum.
Santorum drew fire from Palin for a television interview in which he seemed to suggest Palin was skipping the conference because she would not be paid for appearing.
"I will not call him the knuckle-dragging Neanderthal ... I'll let his wife call him that instead," Palin told Fox News.
The conference resumes on Friday and will include speeches by possible 2012 candidates Mitt Romney, a former Massachusetts governor, and former Minnesota Governor Tim Pawlenty.
Pawlenty will talk about how he cut spending in his state and call on Washington to make similar tough choices, according to excerpts of a speech prepared for delivery on Friday.
"I know something about the spenders and I know something about difficult. I'm from the state of McCarthy, Mondale, Humphrey, Wellstone, and now -- United States Senator Al Franken," he said in reference to prominent Minnesota Democrats.
"But we cut government in Minnesota, and if we can do it there, we can do it anywhere," the excerpt said.
The conference concludes on Saturday with a presidential straw poll. (Editing by Peter Cooney)