AMES, Iowa (Reuters) - Republicans Michele Bachmann and Tim Pawlenty clashed repeatedly over their records during a presidential debate on Thursday, two days before they vie for conservative support in a straw poll that could make or break their campaigns.

The fierce exchanges between the two Minnesotans highlighted a nationally televised presidential debate that also featured heavy criticism of President Barack Obama's economic leadership by eight Republican White House hopefuls.

The debate was the opening act for Saturday's Iowa straw poll, a traditional test of campaign strength in the state that holds the first presidential nominating contest in 2012.

But the debate and straw poll were overshadowed by Texas Governor Rick Perry's plan to enter the race on Saturday, a move that could dramatically reshape the contest and vault him into the top tier of contenders with front-runner Mitt Romney.

In Iowa, Pawlenty is desperately seeking to gain ground on Bachmann, a conservative and Tea Party favorite who leads polls in the state. He wasted little time in ripping into her record in Congress.

"It's an indisputable fact that her record of accomplishment and results is nonexistent," said Pawlenty, the former governor of Minnesota who was criticized when he passed up an opportunity to criticize Romney in the last debate.

He said Bachmann, a U.S. representative from Minnesota, had fought in Congress against spending, against the healthcare overhaul and against other initiatives that had passed despite her efforts.

"She said she's got a titanium spine. It's not her spine we're worried about, it's her record of results," he said. "If that's your view of effective leadership with results, please stop, because you're killing us."


Bachmann responded by attacking Pawlenty's record as governor, including his support for a state cap and trade environmental plan and for individual mandates in healthcare.

"That sounds a lot more like Barack Obama if you ask me," she said.

Pawlenty shot back that Bachmann had "a record of misstating and making false statements."

The repeated clashes between the two contenders caused former Senator Rick Santorum to interrupt at one point and beg moderators of the debate to ask him a question.

The debate's timing two days before the straw poll raised the stakes for several candidates, most notably Pawlenty, who could be fighting for his political life in the nonbinding mock election.

Pawlenty, who has been criticized for being too nice, was more aggressive than he has been on the campaign trail.

He threw a few soft jabs at Romney, who was left alone by the other contenders. Pawlenty made a joke about Romney's wealth and took the opportunity he declined in the last debate to criticize Romney for the healthcare plan he backed while governor of Massachusetts.

That plan has drawn criticism from conservatives as a precursor to Obama's healthcare overhaul, but Romney said there were important differences and "we put together a plan that was right for Massachusetts."

"It's bad law," Romney said of Obama's healthcare plan. "It's bad constitutional law, it's bad medicine."


The candidates all welcomed Perry to the race but had little to say about his candidacy. A staunch social and religious conservative, Perry has a strong job creation record that could cut into Romney's support among the party's pro-business wing.

The debate was the debut on the national stage of former Utah Governor Jon Huntsman, who defended his time as U.S. ambassador to China under Obama. "I'm proud of my service to the country," he said.

Former U.S. House of Representatives Speaker Newt Gingrich condemned some of the questions from the moderators, accusing them of asking "Mickey Mouse" and "gotcha" questions.

All of the contenders battered Obama after last week's downgrade of the U.S. credit rating and days of wild mood swings on Wall Street. "We have, unfortunately, as a leader of this country a man who is out of his depth," Romney said.

Businessman Herman Cain and U.S. Representative Ron Paul also participated in the debate.

Romney warmed up for the debate during a morning visit to the Iowa state fair in Des Moines, where he had a heated exchange with hecklers who pressed him on what he would do to strengthen the Social Security retirement system.

They shouted and chanted "Wall Street greed" as he tried to answer. "If you don't like my answer, you can vote for someone else," Romney said. "I'm not going to raise taxes, that's my answer." He rejected a shouted suggestion that corporations should face higher taxes.

"Corporations are people, my friend," said Romney, the former head of a private equity fund. "Everything corporations earn ultimately goes to people. Where do you think it goes?"

(Additional reporting by Kim Dixon; Editing by Todd Eastham and Sandra Maler)