BEDFORD, N.H. — The Republican presidential candidates were greeted by healthy, and in some cases overflow, crowds Monday as they crisscrossed southern New Hampshire in a scramble to woo voters on the eve of today’s first-in-the-nation primary.

Frontrunner Mitt Romney ended Monday with a rally before 1,400 supporters in Bedford, a Republican stronghold, leaving the former Massachusetts governor’s campaign cautiously optimistic that its unmatched voter turnout operation was poised to help deliver victory. The campaign planned today to make about 34,000 calls to identified Romney voters and monitor about 150 polling places. The campaign expects to compile exit-polling data even faster than media outlets.

“Nobody is doing more voter contact than Mitt Romney right now,” said Jim Merrill, a top New Hampshire adviser. “We have executed our game plan and are pushing everyone for a big turnout.”

Of Romney’s competitors, only Rep. Ron Paul (Texas), who has been running second in most polls, comes close to matching his organizational strength. A Suffolk University daily tracking poll had Romney at 33 percent, Paul at 20 percent, former Utah Gov. Jon Huntsman at 13 percent, ex-Speaker Newt Gingrich (Ga.) at 11 percent and former Sen. Rick Santorum (Pa.) at 10 percent.

Huntsman has been climbing in surveys but did not appear to have a get-out-the-vote operation capable of capitalizing on the second look he was receiving from voters. Gingrich and Santorum also lacked top-flight ground games, although each drew large crowds at several Monday campaign events. One Gingrich event in Hudson was moved at the last minute to accommodate larger-than-expected attendance.

Linda Stone, a 59-year-old from Northfield who grabbed a Gingrich yard sign on her way out of his town hall meeting in Hudson, said she hopes the former Speaker “does well enough” today to compete in South Carolina and beyond. Stone said she would have voted for Romney if Gingrich did not run, because she believes he can beat President Barack Obama in November.

“I have a lot of respect for [Gingrich],” she said. “I think he’s very knowledgeable, very intelligent. I think he knows the issues, probably, as well or better than most of the other candidates. I hope he has the courage to do what he says he wants to do.”

Romney continued to absorb body blows from his opponents, as each sought to boost his finish in the Granite State primary ahead of the important Jan. 21 South Carolina primary. Gingrich and Texas Gov. Rick Perry, campaigning in South Carolina, attacked Romney for his record running the venture capital firm Bain Capital, saying he was responsible for buying companies and laying off employees.

Romney gave his GOP critics ammunition Monday morning when he used some unfortunate wording while telling a gathering of the Greater Nashua Chamber of Commerce that he supports a policy that would enable individuals to more easily switch health insurance companies.

“I want individuals to have their own insurance. That means the insurance company will have an incentive to keep you healthy. It also means if you don’t like what they do, you can fire them,” Romney said. “I like being able to fire people who provide services to me.”

Romney’s opponents jumped on the clumsy phrasing and charged him with being more interested in firing people than creating jobs. Within a couple of hours, Romney held a rare news conference to clarify and repeat the full context of the comments and push back on the criticism he has received on his career at Bain Capital.

But the incident did not appear to dampen enthusiasm among his ardent supporters, at least not in its immediate aftermath, nor did they appear worried that Romney was in danger of losing the primary. Three retirees who attended a Romney event in Hudson on Monday afternoon expressed their support in the type of enthusiastic manner that could bode well for the frontrunner.

Mary Hoppe, of Nashua, said she likes Romney “very much” and said he has grown as a candidate since his disappointing loss to Sen. John McCain (R-Ariz.) in the 2008 Granite State primary four years ago. That’s why she expects him to do well in today’s voting.

“I think [New Hampshire voters] know more about him, and I think that he’s more prepared for the job” of being president, she said.