SIMI VALLEY, Calif. — Quick to tangle, Republican presidential rivals Rick Perry and Mitt Romney sparred vigorously over job creation and Social Security Wednesday night in a feisty campaign debate that marked a contentious new turn in the race to pick a 2012 challenger to President Barack Obama.

Far more than in earlier GOP debates this summer, the candidates mixed it up in their first faceoff since Perry entered the race and almost instantly overtook Romney as front-runner in opinion polls. Those two — as well as other contenders on stage — sniped at one another, contradicted allegations and interrupted media questioners to demand opportunities to take each other on.

“Michael Dukakis created jobs three times faster than you did, Mitt,” Perry jabbed in the debate’s opening moments, referring to one of Romney’s Democratic predecessors as governor of Massachusetts.

“As a matter of fact, George Bush and his predecessors created jobs at a faster rate than you did,” Romney shot back at Perry, the 10-year incumbent Texas governor.

The debate was the first of three in as many weeks, at a time when the economy is struggling, unemployment is seemingly stuck at 9.1 percent and Obama’s popularity is sinking in the polls — all events that could make the GOP nomination worth more than it appeared only a few months ago.

Businessman Herman Cain, Minnesota Rep. Michele Bachmann, Texas Rep. Ron Paul, former House Speaker Newt Gingrich and former Sen. Rick Santorum of Pennsylvania shared the stage for the debate.

Former Utah Gov. Jon Huntsman sided with Perry when he turned to Romney and said, “47th just isn’t going to cut it, my friend,” a reference to the rank Massachusetts had among the 50 states in creating jobs during Romney’s term.

But he also sought to rebut Perry’s claim to be chief executive of the country’s top job-producing state.

“I hate to rain on the parade of the great Lone Star State governor, but as governor of Utah, we were the No. 1 job creator during my years in service,” Huntsman said.

Not surprisingly, the GOP contenders had little good to say about Obama, either his record on creating jobs or the health care law they have vowed to repeal if they win the White House. Perry was an exception, volunteering his praise for the presidential order that resulted in the death of Osama bin Laden in a U.S. military raid in Pakistan. He also said he was happy the U.S. prison at Guantanamo has been kept open.

On another foreign policy issue, Bachmann criticized Obama’s decision to join an international military campaign in Libya.

Bachman also said she would provide the “strong, bold leader in the presidency who will lead” the effort to repeal the health care law passed at Obama’s behest. “None of us should ever think that the repeal bill will just come to our desk,” she said in a pledge that drew applause from the audience.

Gingrich resisted an effort to draw him into conflict with other Republicans on stage. “I’m frankly not interested in your efforts to get Republicans fighting each other,” he said, sparking an even louder round of applause. He said all Republicans should “defeat efforts by the news media” to spark an internal struggle when the real objective is to defeat Obama in 2012.