"You have a choice," Romney, the former governor of Massachusetts, said after ticking off his accomplishments in office. "You can select somebody who wants to fight for those things, or you can select somebody who's actually done those things."
McCain listed the pork-barrel spending he has exposed, as well as an Air Force tanker contract he squashed, before responding: "I think it was a reason why I wasn't elected Miss Congeniality in the Senate. I have a record of saving billions of dollars."
Sitting elbow-to-elbow in a studio on the campus of St. Anselm College, the two rivals also continued a debate they have been conducting at long distance about who is better equipped to bring change to Washington.
"Throughout both Republican debates this weekend, Mitt Romney has been the focus, and that attention has not been at all positive," said CBSNews.com senior political editor Vaughn Ververs. "Both Huckabee and McCain are clearly annoyed by the millions of dollars in ads Romney has run against them. It appears increasingly likely that is was not money well-spent."
Citing his record as a venture capitalist, Olympics CEO and governor, Romney said, "I've been in the economy. I've been in the real world."
McCain shot back moments later: "I led the largest squadron in the U.S. Navy, not for profit but for patriotism."
also jumped into the exchange, mocking Romney for saying the next president did not have to be a foreign policy expert so long as he was a good manager.
"My friend Mitt thinks expertise is important in all areas except national security," Thompson said with a sly smile.
He andscoffed at the notion that change should dominate the political debate - as Thompson noted, just because Iowans said so in their caucuses last week.
Giuliani added, "Change is a slogan, and the examination has to be is it change for good or change for bad?"
There were several prickly exchanges between Romney and rival, the former Arkansas governor who bested him last week in the Iowa caucuses.
At one point, Romney asked Huckabee a question as the former governor was responding to one posed by moderator Chris Wallace. Huckabee said he preferred to speak through the moderator.
Romney also prodded Huckabee about whether spending had increased during his decade as governor of Arkansas.
"You make up facts faster than you can talk sometimes," Romney said as Huckabee avoided giving a direct answer.
Huckabee said: "I had a court order that said we had to improve education."
The debate got under way as a new USA Today/Gallup poll showed the Republican race tied in New Hampshire.
McCain had the support of 34 percent of likely voters, up from 27 percent in mid-December. Romney was at 30 percent, down from 34 percent, and Huckabee - the Iowa caucus winner - was third at 13 percent. Giuliani had 8 percent and Thompson was in the low single digits.
was excluded from the debate by the sponsor, the Fox News Channel. The New Hampshire Republican Party dropped its co-sponsorship of the forum to protest the exclusion.
As the clocked ticked to less than 48 hours before voting began, McCain declared "I will win" Tuesday's primary, while Romney scrambled to keep a second big race from slipping away after posting second in the caucuses.
"I'm planning on winning in New Hampshire," said Romney, but he added, "It may not happen."
Huckabee also downplayed his own prospects but said: "We're going to do better than expected."
The acrimony of their debate Saturday night spilled over into Sunday morning as the top candidates made the rounds of TV news shows before heading out for campaign stops in snowy New Hampshire. They sought to correct their own verbal missteps as well as take swipes at their opponents.
Romney argued that his positions as he runs for president are consistent with the actions he took as governor - despite evidence that he has shifted to the right on some issues. He castigated politicians who he said are more interested in personal insults than changing government - even as his campaign sought to portray McCain as a nasty candidate who has a record of personally going after opponents.
McCain, for his part, tried to walk a careful line.
He didn't mention his opponent during a question-and-answer session at a Salem school, and he mostly resisted engaging in a back-and-forth with Romney when pressed by reporters. He insisted he was focused on running a positive campaign.
McCain, did, however, repeat a claim against Romney that has almost become a standard part of his pitch: "He has changed his position on almost every major issue," McCain said at one point then added: "That doesn't mean he's not a good person."
Projecting confidence, McCain proclaimed in a TV interview: "I will win." Underscoring how much is at stake in New Hampshire, he added that victory is "vital" to his candidacy.
Later on his campaign bus, McCain qualified his prediction of a New Hampshire victory. "I believe I will win, but a lot of things can happen between now and Tuesday when the polls close," McCain said, adding that many New Hampshire Republicans still haven't decided whom to support.
Huckabee spoke of "a brotherhood" of sorts with McCain, fueled by Romney's criticism. "We have both been brutally assaulted by Governor Romney with amazingly misleading ads that attacked and distorted and misrepresented our records, Romney attacking me in Iowa, attacking him in New Hampshire," Huckabee said.
At the same time, Huckabee, who has styled himself as a straight-shooting candidate, confronted his own string of inconsistencies, including recent ones on the troop increase strategy in Iraq, the Writers Guild Strike, and gambling.
"People are going to go through and nitpick. And that's fine," he said. "But I'll tell you why we won Iowa. We won Iowa because people believed that there was a need for somebody who had clarity in his positions. And I've stuck by those positions."
He said he hasn't changed his positions on gun rights, life issues, family values and President Bush's tax cuts. He said he had made some verbal slips but "I think most of us do, especially if we talk as much as politicians do."