|Romney, left, and Perry are the frontrunners in the fight to secure the Republican nomination for president [Reuters]
Republican frontrunner Rick Perry has come under heavy fire on social security, jobs and his record in Texas in a heated US presidential debate as rivals tried to halt the governor's momentum.
Perry, who has soared to the top of opinion polls in the Republican race, renewed his fight with main challenger Mitt Romney on Monday over social security, accusing each other of frightening older people about changes to the country's retirement programme.
The governor, a conservative Tea Party favourite, has zoomed past Romney to lead in opinion polls since entering the race last month.
He frequently drew applause from the conservative crowd at the debate in Tampa, Florida, which was co-sponsored by Tea Party groups that have reshaped the US political scene with their focus on limited government and reduced spending.
Perry's rivals questioned his claims about Texas job creation, his stance on illegal immigrants and an executive order he gave as governor that young girls be vaccinated for a sexually transmitted virus that causes cervical cancer, the latter which he admitted was a mistake,
The lively exchanges and repeated focus on Perry reinforced his growing stature as the candidate to beat in the 2012 race for the nomination to challenge President Barack Obama.
Perry was often on the defensive, easing back from his earlier comments on social security and the Federal Reserve and deflecting criticism where possible.
He softened his harsh criticism of the retirement programme and said he wanted to start "a legitimate conversation" about its future.
Last week, Perry called the program a Ponzi scheme and a "monstrous lie".
"The term Ponzi scheme I think is over the top and unnecessary and frightful to many people," said Romney, the former Massachusetts governor, who pressed Perry on whether he still believed the retirement programme should be shifted to states and ended as a federal programme.
"We're not going to take that programme away," Perry said.
"Rather than trying to scare seniors, like you're doing and other people, it's time to have a legitimate conversation about how to fix that program so it's not bankrupt."
The social security debate will be watched closely in Florida, which has the country's second-biggest proportion of elderly voters and hosts a crucial nominating contest next year.
"We're frightening the American people, who just want solutions," said Jon Huntsman, the former Utah governor, adding that Republicans could not win an election by promising to dismantle social security.
"We've got the answers, we don't have leaders," he said.
Former US House of Representatives speaker Newt Gingrich said he was not worried about Romney and Perry frightening older people "when President Obama scares them every day".
Polls show the Tea Party is viewed favourably by about 20 to 30 per cent of US citizens.
Al Jazeera's Andy Gallacher, reporting from Tampa, said: "... within the political parties their [the Tea Party] voice is very loud indeed. And they did play that vital role in last year's mid-term elections.
"I think going ahead, all of these eight candidates, and any of the ones that enter the race, certainly know that they will need this grass-roots political movement support ... to become that one person who will go on and challenge US President Barack Obama."
US Representative Michele Bachmann, whose campaign has faded badly in the last month after winning a straw poll in Iowa, targeted Perry over his executive order on the vaccine programme in Texas.
She accused Perry of issuing the order because his former chief of staff was a lobbyist for Merck & Co, the company that made the drug.
"Was this about life, or was it about millions for a drug company," asked Bachmann, who has seen Perry rob her of much of her religious and social conservative support.
Perry said Merck gave him a $5,000 donation. "If you're saying that I can be bought for $5,000, I'm offended," he said.
Bachmann shot back: "I'm offended for all the little girls and the parents who didn't have a choice."
Romney said Perry's record on job creation in Texas, which has outpaced most other states in adding new jobs, was the result of Texas' lack of an income tax, natural resources and other factors rather than his policies.
"I think Governor Perry would agree with me that if you're dealt four aces that doesn't make you necessarily a great poker player," Romney said.
Perry tempered earlier comments targeting Federal Reserve Chairman Ben Bernanke, but again said it would be "almost treasonous" to allow the central bank to be used for political purposes.
Those comments were turned back on him later during a discussion of his opposition to a border fence in Texas.
"For Rick to say you can't secure the border is pretty much a treasonous comment," Huntsman said, playing off Perry's Bernanke comments, which caused a stir last month.
Other candidates participating in the debate were businessman Herman Cain, US Representative Ron Paul and former US senator Rick Santorum.
In regards to who won the debate, Gallacher said: "As for clear winners, there really wasn't one."
"We saw Michelle Bachmann, the darling of the Tea Party make quite an aggressive stand as she really needed to do that because she's falling behind in the polls.
"But really it was mostly about Mitt Romney and Rick Perry."
The debate was the fifth of the Republican presidential campaign. It will be followed by another debate next week in Orlando, Florida, as the White House race heats up.