Newt Gingrich took his turn in the sweat box as the latest Republican presidential front-runner during a nationally televised debate in Iowa Saturday, with time running out for rivals to stop his ascendancy before the state's Jan. 3 caucuses begin the nomination process.

The former House speaker surged to a wide lead in recent polls over Mitt Romney, long considered the most likely victor in the race to choose a GOP challenger to President Obama in 2012, but he came under attack during the early stages of the debate.

"Speaker Gingrich has been in government a long time," said Romney, who argued that his career as an investment banker in the private sector is his biggest credential. Asked where he differs from Gingrich, Romney said, "We could start with his idea for a lunar colony to mine minerals from the moon" and to "remove the child-labor laws" so poor children can work as janitors in their schools.

"The only reason you're not a career politician is because you lost to [the late Sen.] Teddy Kennedy in 1994," Gingrich said, referring to Romney's unsuccessful Senate campaign.

As Gingrich has risen, Romney, through surrogates and a supportive PAC, has attacked Gingrich as insufficiently conservative on some key issues as well as bombastic and perhaps unstable.

In that vein, the two sparred over the uproar caused by Gingrich's recent statement on a Jewish cable television network that the Middle East peace process is "delusional" and that the Palestinians are "an invented people."

Romney portrayed the remark as irresponsible and destabilizing. "If I am president I will exercise sobriety, care and stability. . . . I'm not a bomb thrower, rhetorically or literally."

Gingrich shot back that he was simply telling the truth. "This is a propaganda war . . . you're not going to win in the long run if you're afraid to stand firm and stand for the truth," he said.

Romney drew fire as well, for a law he pushed through in Massachusetts as governor that requires people to buy health insurance - a model for Obama's health program. The issue led to what may have been the first wager offered in the middle of a presidential debate.

Texas Gov. Rick Perry contended that Romney had changed wording about the mandate between editions of his book, downplaying it.

"Rick, I'll tell you what, $10,000?" Romney said, stretching out his hand toward a stunned Perry. "$10,000 bet?"

Perry recovered, saying, "I'm not in the betting business."

Democrats gleefully cited the bet as proof the wealthy Romney is out of touch with typical Americans, for whom $10,000 would be several months' salary. (They did not mention that Romney's Mormon religion forbids gambling.)

Rep. Ron Paul of Texas ripped Gingrich for earning $1.8 million as a consultant for the quasi-government mortgage giant Freddie Mac, which he and other conservatives have blamed for the housing price crash, saying that was essentially "taxpayer money."

Minnesota Rep. Michele Bachmann called Gingrich the "epitome of the establishment" who worked on K Street, "taking money to influence the outcome of legislation." But she also spoke of "Newt Romney," pointing out that both men had supported government requiring individuals to buy health insurance, as well as the bank bailouts.

Gingrich said he did not lobby for Freddie Mac but provided "strategic advice" much as management consultant firms do. "You get to charge money for that," Gingrich said. "It's called free enterprise."

The two-hour debate was broadcast on ABC and moderated by Diane Sawyer and George Stephanopoulos. Yahoo, the Des Moines Register, and the Iowa Republican Party also sponsored the debate.

It was the 12th televised debate for the Republican candidates this year, and they are scheduled to meet again Thursday in Sioux City, Iowa.

Compared with some of the other gatherings, it was downright cozy, with just six candidates on stage at Drake University, one week after pizza executive Herman Cain quit the race amid accusations of serial sexual misconduct, including several harassment complaints by female employees from his time as head of the National Restaurant Association in the 1990s. Former Utah Gov. Jon Huntsman, who has not campaigned much in Iowa, was not doing well enough in state polls to qualify for the debate.

In addition to Gingrich, Romney, Perry, Paul, and Bachmann, the debate included Rick Santorum, former U.S. senator from Pennsylvania.

Gingrich, whose campaign almost collapsed in the summer, has risen suddenly in the polls, taking advantage of the opening left by Cain's departure in the rotating search for an alternative to Romney for conservatives who just don't warm to the former Massachusetts governor. Romney has disavowed some earlier moderate positions, such as supporting abortion rights and gay rights, in a party dominated by the right.

Gingrich had the support of 25 percent of likely caucus voters in the latest Iowa Poll from the Des Moines Register. Paul was second with 18 percent, followed by Romney at 16 percent. Eleven percent were undecided, the poll found - and 60 percent of those supporting a candidate said they could change their mind before caucus day. The poll has a margin of error of plus or minus 4.9 percentage points.

Cain was briefly the Not-Mitt, as were Perry and Bachmann, but each faded.

Later, Gingrich's personal history - he is on his third marriage and has admitted to infidelity in the past - came up indirectly, as the candidates were asked whether fidelity to one's spouse is an appropriate issue in the campaign.

Santorum said it was not an automatic disqualifier but was a factor voters should consider because it "goes to the core of who you are."

Gingrich agreed. "I said up front openly, I've made mistakes at times," he said. "I've had to go to God for reconciliation. . . . I think people have to measure who I am now and whether I'm a person they can trust."

Contact politics writer Thomas Fitzgerald at 215-854-2718 or tfitzgerald@phillynews.com or @tomfitzgerald on Twitter. Follow his blog, "The Big Tent," at www.philly.com/BigTent.