Mitt Romney holds a formidable lead in New Hampshire heading into the final days of campaigning before Tuesday’s primary and has solidified his position in the crucial battleground state of South Carolina, according to new polls, with his rivals looking to a pair of weekend debates to knock the GOP front-runner off his stride.

Romney’s path to the nomination is aided by the fact that conservative Republicans who oppose him have not yet coalesced around a candidate. Former senator Rick Santorum of Pennsylvania, who barely lost to Romney in Iowa, is looking for a clear second-place finish in New Hampshire to propel him into South Carolina as the principal alternative to Romney.

Romney’s growing strength, aided by his narrow victory Tuesday in the Iowa caucuses, added a sense of urgency to his rivals’ efforts to find a way to slow the former Massachusetts governor’s momentum, which threatens to bring an early conclusion to the nomination battle.

The candidates will debate twice this weekend, giving Romney’s rivals ample opportunity to make the case against him. The first debate will be Saturday night, hosted by ABC News and WMUR-TV. On Sunday, the candidates will face off on NBC’s “Meet the Press,” a forum co-hosted by the New Hampshire Union Leader.

There were signs Friday that Santorum could emerge with a second-place finish in New Hampshire. But with former House speaker Newt Gingrich and Texas Gov. Rick Perry still in the race, to say nothing of Rep. Ron Paul (Tex.), Santorum is waging a battle to claim the conservative mantle while at the same time trying to make the case against Romney.

Santorum came under sharp attack Friday. Sen. John McCain (Ariz.), traveling with Romney, again hammered Santorum for supporting earmarks as a senator, saying the two have had “a strong disagreement” over pork-barrel projects.

Santorum fired back, arguing that federal spending is out of control because of entitlement programs, not earmarks, which are a small fraction of the budget. Campaigning in Dublin, N.H., he defended his support for earmarks by saying he was elected “to represent the interests of Pennsylvania.”

Meanwhile, Paul launched an ad in South Carolina attacking Santorum as “a corporate lobbyist and Washington politician” who has compiled “a record of betrayal.”

Santorum also ran into heckling later in the day from protesters who appeared to be a combination of gay rights activists, Ron Paul supporters and people from the Occupy movement.

Romney started with a morning rally in South Carolina that featured McCain and Gov. Nikki Haley. He ended the day with a spaghetti-dinner rally in tiny Tilton, N.H.

With his eye on President Obama, Romney brushed aside new government statistics showing a small tick down in the unemployment rate, to 8.5 percent. He argued that the president’s policies have failed and that he should be replaced next November. Calling the president a believer in “crony capitalism,” Romney said, “He has failed to put Americans back to work. ”

As he campaigned, a new CNN/Time/ORC poll of Republicans in South Carolina showed Romney with a 2-to-1 lead over Santorum and Gingrich after trailing Gingrich by 2-to-1 in a poll taken in early December.

The dramatic shift in sentiment, which has been common in the Republican race, affected all three top candidates. Romney’s support rose by 17 percentage points to 37 percent, and Santorum’s jumped from 4 percent to 19 percent. Gingrich, meanwhile, saw his support cut in half, from 43 percent to 20 percent.

Those numbers are likely to change after New Hampshire votes on Tuesday.

Romney returned to New Hampshire to find two new polls underscoring his advantage there. A survey by the University of New Hampshire for WMUR-TV put Romney at 44 percent, a gain of five points in two weeks. Paul ran second at 20 percent. Santorum was at 8 percent in the WMUR poll, tied with Gingrich, but he had gained strength while Gingrich had fallen since the previous survey. Former Utah governor Jon Huntsman Jr., who has staked his candidacy on New Hampshire, was at 7 percent.

Pollster Andrew Smith said Santorum’s support in the survey nearly tripled in the days after the Iowa caucuses and predicted that the former senator could challenge Paul for second place in the Granite State.

A new NBC News/Marist poll also showed Romney with a sizable lead. Romney led with 42 percent, followed by Paul at 22 percent and Santorum at 13 percent. Gingrich and Huntsman were each at 9 percent.

Huntsman began his day speaking to college students and played down his low standing. “If you don’t light your hair on fire and if you don’t sign those silly pledges and you don’t have all these ‘oops’ moments, you’re not going to get as much airtime,” he said. He said he was confident that when people finally vote, he will be seen as more presidential than his rivals.

“This isn’t a caucus,” he said. “This is a primary. It’s the real deal.”

Gingrich was in full professor mode for part of the day, appearing at Dartmouth-Hitchcock Medical Center in Lebanon, where he opened his talk with a reference to the Wright Brothers and closed it with a mention of Abraham Lincoln.

But Gingrich did make time for politics Friday, pushing his case that he is the best GOP candidate to take on Obama on the debate stage and claiming that Romney is a moderate, rather than a true conservative.

Paul, who finished a close third in Iowa, arrived in the state Friday afternoon after two days off the trail. He was greeted by hundreds of cheering and chanting supporters packed into a hangar at the Nashua airport. “All I can think about is, freedom is popular!” Paul told the faithful.

Weiner reported from South Carolina. Staff writers Joel Achenbach, Nia-Malika Henderson and Rosalind S. Helderman in New Hampshire contributed to this report.