MANCHESTER, N.H. - Mitt Romney's rivals hoped to seize on back-to-back debates this weekend to knock the front-runner off stride and gain momentum heading into Tuesday's New Hampshire primary and upcoming contests later this month in the South.

Romney, who narrowly beat Rick Santorum in Iowa this past week, had the most to lose in the debates Saturday night and Sunday morning as the other Republicans in the race try to prevent him from running away with the nomination.

Santorum, Newt Gingrich and Rick Perry were competing to emerge as the conservative alternative to Romney. Jon Huntsman and Ron Paul were fighting for relevancy.

The debate at Saint Anselm College was the first in more than three weeks, and the first since Michele Bachmann dropped out of the race after a disappointing finish in Iowa this past week. The candidates faced a quick turnaround for the second debate, set for this morning in Concord.

Romney, a former Massachusetts governor, has largely escaped setbacks in the previous 13 debates, but he has faced intensifying criticism from the other candidates in recent days.

Gingrich, who had promised to run a positive campaign, was the leading agitator and hours before the debate, the former House speaker showed no signs of relenting.

"I do think there's an enormous gap between somebody who is a bold Reagan conservative and somebody who is a timid Massachusetts moderate," Gingrich told voters in Wolfeboro, where Romney has a summer home. Gingrich this past week added a "Not Romney" section to his campaign website, http://www.newt.org/notromney

Recent polling gave Romney strong leads in New Hampshire and South Carolina, which hosts the next nominating contest Jan. 21, followed by Florida on Jan. 31. A presidential contender has never won the first three contests.

The candidates have campaign aggressively in New Hampshire, trying to make their case with voters who are notoriously late deciders.

"I'm looking to finalize my decision. The debate will pretty much determine who I'm voting for on Tuesday," said Ed Cormier, 58, of Rochester. "I keep hearing how Romney's the most electable. I like Romney, but he's not my first choice."