STRATHAM, N.H. - The Republican presidential contest heated up Thursday, as Mitt Romney formally launched his candidacy from a windswept Yankee farm amid intensifying criticism from potential rivals.

In his second try for the nomination, Romney, 64, is casting himself as a seasoned crisis manager for a nation "in peril." He laced his remarks with a sharp attack on President Obama, pledging to spark an American economic revival by slashing federal spending, lowering business taxes, and balancing the budget.

"I'm Mitt Romney. I believe in America, and I'm running for president of the United States," the former Massachusetts governor said to cheers from several hundred supporters.

In keeping with the casual style of his 2012 campaign, he spoke, shirtsleeves rolled up, from a flatbed trailer. He was introduced by his wife, Ann, as he was when he declared his candidacy in his native Michigan four years ago.

This time, Romney is better known and leading in national polls, though the vast majority of Republican voters have yet to focus on the race. A shifting field of foes is already taking aim, showing no qualms Thursday about stepping on his big day.

Before he finished speaking, former Alaska Gov. Sarah Palin had rolled into a nearby New Hampshire town, trailed by the phalanx of reporters and cameras that has tracked her bus up the East Coast this week. Two other potential GOP candidates, former New York Mayor Rudolph W. Giuliani and Michigan Rep. Thaddeus McCotter, also competed for media and voter attention in the state.

Romney tried to take the developments in stride. Asked by a reporter about Palin's arrival, he said: "I think it's great. New Hampshire is Action Central today."

Palin, whose flirtation with a presidential run isn't taken seriously by most GOP strategists, swung hard at Romney's health-care record, perhaps his biggest vulnerability in the nomination fight. Conservatives strongly oppose the Massachusetts medical-insurance requirement Romney signed into law as governor, which became a model for the national mandate enacted by Obama and congressional Democrats last year.

"In my opinion, any mandate coming from government is not a good thing," Palin said during a stop in Massachusetts before heading north. Giuliani, who competed for the Republican nomination in 2008, echoed her criticism in a speech in North Conway, N.H.

In his remarks, which lasted no more than 20 minutes, Romney referred fleetingly to the Massachusetts health-care system, defending it as "a state solution" to the problem of the uninsured.

For the most part, he zeroed in on the general election, avoiding Republican foes and primary-campaign topics - such as abortion - that were part of his 2008 announcement speech.

"Barack Obama has failed America," he said. "Mr. President, you've had your turn."

He said the incumbent had prolonged the economic downturn and made it worse. Romney assailed what he described as Obama's "distrust" of Israel, uncertain response to the democratic awakening in Arab countries, and flawed Afghanistan policy.

In 2008, New Hampshire helped sink Romney's White House hopes. He lost the state to eventual nominee John McCain in an upset, after an expensive investment of time and money. This time, polls show Romney far ahead, though Granite State voters have a penchant for confounding expectations.