MANCHESTER, N.H. - Republican presidential candidates Mitt Romney and Mike Huckabee exchanged sharp words as they opened a Saturday evening debate with a heated argument about foreign policy.

Romney criticized Huckabee for writing that President Bush's foreign policy has "an arrogant bunker mentality," prompting a feisty Huckabee to accuse Romney of once supporting a timed withdrawal from Iraq.

"Governor, don't try to characterize my positions," Romney retorted.

"Which one?" the former Arkansas governor shot back, prompting Romney to accuse Huckabee of engaging in a personal attack.

Host Charles Gibson had sparked a six-way argument by asking whether the candidates support Bush's policy of pre-emptive war. The leading candidates all embraced the policy, then ganged up on Texas Rep. Ron Paul for repeating his belief that terrorism is sparked by U.S. foreign policy.

Romney and Arizona Sen. John McCain are engaged in a high-stakes battle to win New Hampshire's primary Tuesday.

In the first half-hour, Gibson sought from the candidates a statement of the principles on which they would base their presidencies. Later, the group discussed how to provide health-care coverage to the uninsured, prompting a sharp exchange between McCain and Romney over the role of drug companies.

"Don't turn the pharmaceuticals into the big, bad guys," Romney said.

"They are," McCain said.

The 90-minute debate, held at St. Anselm College, was hosted by ABC News and the Facebook Web site. Former New York Mayor Rudy Giuliani and former Tennessee Sen. Fred D. Thompson also participated.

Romney is trying to cast himself as the only outsider willing to take on corruption and special interests. He paints McCain as an entrenched politician who represents the status quo.

McCain and Romney clashed even before the debate, both seeking an advantage in a state where a loss could end their presidential hopes.

Romney hopes to convince voters that he is the Republican equivalent of Barack Obama and John Edwards -- the only candidate who can bring radical change to a Washington establishment mired in bureaucracy and old thinking.

Get $150+ in coupons in every Sunday N&O. Click here for convenient home delivery.