MANCHESTER, New Hampshire — A pair of weekend debates could be the last chance for conservative Republican presidential hopefuls to prove who is the best alternative to frontrunner Mitt Romney ahead of next week's New Hampshire primary.

Former Pennsylvania senator Rick Santorum, fresh off his nail-biter loss to Romney in the Iowa caucuses, will find himself in prime position closer to the center of the debate stage -- and will come under new fire from his rivals.

Former House speaker Newt Gingrich, who blamed his disappointing fourth-place Iowa finish on attack ads by Romney and his allies, can be expected to show no mercy in going after the former Massachusetts governor.

Texas Governor Rick Perry meanwhile will need to unleash some memorable zingers to help resurrect his flagging campaign after an embarrassing fifth-place Iowa showing.

The debates are going to be "highly negative," said Larry J. Sabato, a politics professor at the University of Virginia and the author of "Feeding Frenzy: Attack Journalism and American Politics."

"It's 10 minutes to midnight. If Romney runs away with the voting, there may be no stopping him," Sabato said.

Romney leads in both national and New Hampshire polls for the Republican nomination and the chance to go up against President Barack Obama in the November general election.

In the tiny northeastern US state, Romney draws 41 percent support among likely primary voters, according to a two-day tracking poll by Suffolk University/7News released Thursday.

Texas congressman Ron Paul is a distant second at 18 percent, followed by Santorum at eight percent, Gingrich and former US ambassador to China Jon Huntsman at seven percent, and Perry struggling to even get one percent.

Just as the Iowa caucuses prompted Minnesota congresswoman Michele Bachmann to quit the race, a poor showing in New Hampshire could send another candidate packing.

The Saturday and Sunday debates could thus prove pivotal in determining who survives and heads to South Carolina and Florida, the final nominating contests in January.

Roger Hammarberg is one of the 17 percent of likely Republican primary voters in New Hampshire who have yet to choose a candidate.

"I'm torn between Gingrich and Romney," the 63-year-old retired physical therapist from Bethlehem said at a Gingrich town hall meeting on Thursday in snowy Littleton.

"They are the most electable. I haven't ruled out Santorum, but I don't think he can stand up to Obama. I'll be watching the debate and be open to being surprised."

Thus far in the race, the debates -- featuring gaffes by Perry and Romney's $10,000 bet to the Texas governor -- have influenced the pecking order of the field, says presidential debate expert Allan Louden of Wake Forest University.

"Romney needs to stay cool and look presidential," Louden said. "Gingrich has to get Romney to make mistakes. If Gingrich tries to be Mr. Nice Guy, he loses. He needs to get Romney flustered."

Gingrich, when asked Thursday what he hopes to accomplish in the debates, answered coyly, "Clarity."

That was perhaps a hint he will take to the debate stage his new sharp attack on Romney in New Hampshire, unveiled in both a newspaper and TV ad, in which he contrasts their positions on taxes, guns and abortion.

Perry's New Hampshire spokesman Paul Young said the Texas governor's goal will be to cast himself as "the non-Washington insider who can create jobs."

Michael Traugott, a political science professor at the University of Michigan, highlighted the importance of pithy one-liners.

"A memorable line can determine whether you are mentioned at the top of a story rather than at the bottom," said Traugott, singling out Bachmann for cleverly merging Gingrich and Romney in a debate last month by repeatedly calling them "Newt-Romney."

Erika King, a politics professor at Grand Valley State University, says Santorum needs to seize the debates to define himself.

"There is going to be a tremendous focus on him," King said.

"He has to not make any mistakes. And he has to introduce himself to the wider American public because nobody was paying any attention to him in earlier debates. He needs to move from social conservatism to an economic message."

Stephen Hess, a presidential scholar at the Brookings Institution, expects debate interest to grow now that the voting has begun.

"I think part of the reason the debates have been popular is they come at a time of reality shows," Hess said.

"They aren't that different than the 'Jersey Housewives,'" he added, referring to the popular TV reality show, "The Real Housewives of New Jersey."

"The debates have been engaging, with unusual characters to keep the audience interested."