Criticism of Romney zeroed in on whether the former governor of a moderate New England state would be the strongest candidate to fly the conservative flag against Obama in the November election.

Gingrich, hurt by a spate of negative ads organized by former Romney staffers, said Romney would "have a very hard time getting elected" and had policy positions that are not sufficiently different from Obama.

"There's a huge difference between a Reagan conservative and somebody who comes out of the Massachusetts culture who essentially has a moderate record," Gingrich said during the NBC/Facebook debate in Concord, New Hampshire.

But Romney defended himself as "a solid conservative" who was in politics on a detour from his business career as a venture capitalist. Acting like a front-runner, he kept his focus more on Obama than on his Republican rivals.

"I happen to believe that if we want to replace a lifetime politician like Barack Obama ... we've got to choose someone who is not a lifetime politician, who has not spent his entire career in Washington."

Gingrich bristled at Romney's attempts to paint himself as a reluctant politician.

"Can we drop a little bit of the pious baloney?" he quipped. "You were running for president while you were governor."

Hard Choices over Candidates

In the most tumultuous nominating process in the Republican camp in decades, it is hard to know what voters want - a flagbearer of conservative values or a serious challenge to a vulnerable incumbent trying to revive the sagging US economy.

Sue Grant, 49, was one of those torn New Hampshire voters, "on my knees praying," as she struggled to make a decision on her candidate. Romney appeared to be off her list.

"He does not make me warm and fuzzy," Grant said. "I want somebody that is separate from the same old get along and go along wishy-washy."

Santorum is running hard on his socially conservative credentials and used the spotlight again on Sunday to reinforce that message. He also emerged unscathed from an exchange about gay rights.

Santorum "has accepted the fact that he's going to lose New Hampshire, maybe badly. He spoke more to South Carolina than to New Hampshire," Sabato said.

Santorum has been riding a wave of popularity after a narrow second-place finish to Romney in the first Republican presidential nominating contest in Iowa last week.

Often in the news for negative comments about gays, Santorum managed to strike a conciliatory tone, saying "every person in America, gay or straight" should be treated with respect and that he would still love a gay son.

One of the biggest applause lines came from Jon Huntsman, who responded to a comment Romney had made about him in Saturday night's debate in Goffstown, New Hampshire.

Romney had slapped Huntsman for "implementing" Obama's agenda as US ambassador to China, a post he held until April.

Addressing debate moderator David Gregory, Huntsman said: "This country is divided, David, because of attitudes like that. ... The American people are tired of partisan divisions."

"There are five candidates (with) a shot at getting double digits in New Hampshire and I think they all helped themselves today," said Fergus Cullen, former chairman of the New Hampshire Republican Party.