Defending his previous criticism that the Bush administration's foreign policy is "arrogant" and a "bunker-mentality," Huckabee attacked his Republican rival, suggesting he has better foreign policy bona fides.
"I supported the surge before you did," Huckabee said.
"I also supported the troop surge," Romney shot back.
The debate is also expected to highlight the political collision between Sen. John McCain, R-Ariz., who is looking strong in the state after his campaign all but collapsed this summer, and former Romney, who is working to win the support of Granite State voters after a searing loss in Iowa.
The latest WMUR/CNN poll released just hours before the debate began has McCain leading Romney in the Granite State by 6 percentage points, with the Arizona senator at 33 percent support and the former governor at 27 percent support.
Former New York Mayor Rudy Giuliani garnered 14 percent. He has made frequent visits to the state and spent $2.5 million on television advertising there, according to data from the Campaign Media Analysis Group, an independent organization that tracks campaign spending.
Former Arkansas Gov. Mike Huckabee, whose popularity among evangelical Christians helped him win the GOP caucus in Iowa, showed 11 percent support in New Hampshire, according to the WMUR poll.
The former Baptist minister had campaigned in New Hampshire, and his support for tax increases as Arkansas governor and his brand of economic populism isn't an easy sell with voters in the anti-tax, anti-big government state.
While Huckabee intends to campaign hard in New Hampshire until Tuesday, his next real test is the Jan. 19 South Carolina primary, where his prospects look better.
"We're going to have to go convert a lot of people in New Hampshire in the next five days. A big tent revival out on the grounds of the Concord state capital," Huckabee told ABC News senior political correspondent Jake Tapper.
Other Republican candidates have hardly registered a blip on the radars of voters in the state. The latest poll has Rep. Ron Paul, R-Texas, at 9 percent support, and former Sen. Fred Thompson of Tennessee and Rep. Duncan Hunter, R-Calif., tied with 1 percent support each.
Romney, the former governor of a neighboring state, has poured resources into New Hampshire, spending millions of dollars in the Granite State on television ads and building a campaign infrastructure. He has not detailed to reporters how much of his own fortune was spent there.
McCain, who defeated George W. Bush in the New Hampshire primary in 2000, has an edge among the state's independent voters.
And in a state that has a history of making or breaking presidential runs, candidates are pushing through exhaustion after Iowa, trying to woo the state's crucial independent voters with a message of "change."
The race has turned ugly between Romney and McCain, with the former Massachusetts governor trying to paint the Arizona senator as a Washington insider.
"It's one thing to say it; it's another thing to do it," Romney said Saturday in Derry, N.H., arguing his record in business and government proves he can overhaul a dysfunctional Washington.
McCain countered Saturday, "I am responsible for the biggest change that has saved American lives," he said, referring to his years-long call for the troop surge strategy in Iraq.
Romney has also begun hammering the Arizona senator with a steady stream of negative ads in the state.
One such ad says, "He [McCain] even voted to allow illegal immigrants to collect Social Security."
But Romney did gain new delegates Saturday, winning the Wyoming Republican caucus, giving him most of the 12 delegates at stake there.
Candidates debate tonight knowing New Hampshire may reset a Republican presidential contest that has yet to find its front-runner.
All of the major candidates from each presidential party will meet face-to-face in two debates that will air on ABC 30 Saturday night.
The debate will look very different from the those we've seen so far. Only the leading candidates will be there, they'll sit around a table - and for the first time, they'll be encouraged to address each other.
You can watch Saturday night's Democratic and Republican debates on ABC 30 starting at 7 o'clock.