SIOUX CITY, Iowa — Newt Gingrich found his record challenged repeatedly in a high-stakes debate Thursday, the last chance for him and his rivals to appear together in a televised debate before voting for the 2012 Republican presidential nomination starts in less than three weeks.

Gingrich, who had surged to the lead in first-voting Iowa, insisted that he did nothing wrong in taking money from the federal housing agency Freddie Mac.

He also brushed aside questions about whether his record would make him a weak general election challenger to President Barack Obama.

He likened himself to Ronald Reagan, noting that Reagan at this stage in 1979 trailed President Jimmy Carter by 30 percentage points and went on to debate Carter and win in a landslide.

“I believe I can debate Barack Obama,” Gingrich said. “Barack Obama will not have a leg to stand on.”

The two-hour debate, televised by Fox News from the Sioux City Convention Center, was the 13th debate of the campaign and the last before Iowa Republicans kick off the voting for a nominee with precinct caucuses on Jan. 3.

Gingrich, the former speaker of the House of Representatives, found himself at center stage among seven candidates thanks to his lead in polls here.

Asked about criticisms that he is not sufficiently conservative, he called the charge “laughable.” He said he had a 90 percent grade for his congressional voting record from the American Conservative Union, noting such successes as balancing the budget, passing welfare reform and cutting taxes.

He did not contest a question about whether he’s changed positions on issues over the years – Iowa ads from rivals slam him for flipping on such issues as global warming. “I do change things when conditions change,” he said.

Others also argued why each would be a better challenger – or alternative – to Obama.

Rep. Ron Paul of Texas laughed at the question about whether he would be better or worse than his rivals at defeating Obama.

“Anybody up here could probably beat Barack Obama. The challenge isn’t all that great … he’s beating himself,” Paul said.

Instead, he said, voters should consider what the winning Republican would do in office. “I have something different to offer,” he said, mentioning his support for civil liberties, his opposition to military interventions overseas, and his vow to cut $1 trillion out of the budget the first year.

Former Massachusetts Gov. Mitt Romney said he’d be the strongest general election candidate because of his record in business.

“I’ve spent my life, my career in the private sector. … I can debate President Obama based on that understanding,” he said. “I know what it takes to get this economy moving, the president doesn’t.”

Romney also defended his record of investing in businesses, even those that laid off workers. “We did our very best to make those businesses succeed,” he said.

Texas Gov. Rick Perry, seeking a comeback after stumbles in earlier debates, insisted that he’s getting better and could take on Obama in general election debates.

“I’m kind of getting to the point where I like these debates,” he said. “We will get it on,” he said of a potential faceoff with Obama. “I’ll talk about what we did in Texas … about a balanced-budget amendment … about a part-time Congress.”

He also likened himself to Denver Broncos quarterback Tim Tebow, known for his Christian faith and for last-minute comebacks.

“Am I ready for the next level? I hope I am the Tim Tebow of the Iowa caucuses,” Perry said.

Also participating were: Rep. Michele Bachmann of Minnesota, former Utah Gov. Jon Huntsman and former Pennsylvania Sen. Rick Santorum.