By Steve Holland
ORLANDO, Florida (Reuters) - Republican Rick Perry goes into a presidential debate on Thursday looking to put some distance between himself and rival Mitt Romney and position himself as an electable alternative to President Barack Obama.
Perry, Romney and a gaggle of lesser rivals take the stage on Thursday night in the third in a series of debates aimed at helping Republicans decide who they want as their nominee to face the Democrat Obama in the November 2012 election.
So far Perry, the Texas governor and Tea Party movement favorite, holds the front-running position but the lead is considered fragile over Romney, a former Massachusetts governor and the choice of many mainstream Republicans.
Republicans increasingly see a good chance to oust Obama from the White House with the U.S. economy struggling to rebound from 9.1 percent unemployment and chronic debt and deficits.
Perry has delighted Tea Party movement conservatives, but he has raised eyebrows among moderate voters by denouncing the Social Security program as a "Ponzi scheme" and condemning Federal Reserve Chairman Ben Bernanke as "almost treasonous."
"I still think he has to tone down some of his rougher edges," said Republican political analyst Ari Fleischer, who was press secretary to former President George W. Bush.
"Running for president is different than running for governor. People want to feel a sense of inspiration as well as ideological attraction," Fleischer said.
Romney is trying to portray Perry as too far out of the mainstream, while Perry wants to make Romney appear little different from Obama.
The two men are expected to clash anew over Social Security, healthcare and jobs. A USA Today/Gallup poll on Wednesday found Perry leading Romney 31 percent to 24 percent among Republican likely voters.
"We need to nominate someone who will have a stark, clear difference between the Republican nominee and President Obama," Perry told the Fox News Channel.
"And I think I am that person who can clearly delineate the differences. We don't need to nominate 'Obama-lite.' We don't need to nominate someone who's going to blur the lines between President Obama and our nominee," Perry said.
Each man has stepped up their rhetoric in recent days and more fireworks are expected at the debate in Florida, where senior citizens who make up a large percentage of the state's population are wary of any changes to the government retirement programs.
The two-hour debate, sponsored by Fox News and Google, begins at 9 p.m. EDT.
"I continue to think that the Republican race is remarkably fluid and Republican primary voters are still in a shopping mode," said Fleischer. "There's no doubt that there are two leading contenders. But their leads are built on sand, not stone."
The debate may be significant for candidates who have appeared to be fading in recent weeks, including Minnesota U.S. Representative Michele Bachmann, who has been hurt most by Perry's rise, and former U.S. ambassador to China Jon Huntsman, a moderate who has failed to catch fire.
(Additional reporting by JoAnne Allen in Washington; Editing by Vicki Allen)