* Unofficial kickoff to New Hampshire primary
* Romney to Obama: Why did you call me over healthcare? (Updates throughout with speeches)
By Steve Holland
MANCHESTER, N.H., April 29 (Reuters) - Republican presidential hopefuls jockeyed for position and took turns assailing President Barack Obama at an event on Friday that illustrated the wide-open race for the party's 2012 nomination.
The event, sponsored by the Americans for Prosperity Foundation, marked the unofficial start to New Hampshire's first-in-the-nation primary race next year. New Hampshire traditionally follows the Iowa caucuses and its voters pride themselves on vetting presidential candidates.
While all five Republicans espoused conservative values and blamed Obama for a struggling economy and high gas prices, two participants were singled out to defend policies now opposed by conservatives.
Former Massachusetts Governor Mitt Romney, whom some analysts call the front-runner in the Republican race, defended a healthcare policy for his state that Democrats like to say Obama used as a model for his national healthcare overhaul.
"I went to work trying to solve a problem," Romney said when the moderator asked him about it. "It may not be perfect."
He called Obama's plan "unconstitutional" and one that will bankrupt the country.
"If and when I have the occasion to debate President Obama, I'm going to ask him this question: 'Mr. President, why didn't you call me and asked how it worked?' Mine was an experiment, some parts didn't work," he said.
Many conservatives believe Romney's healthcare plan is an Achilles' heel for his candidacy.
Former Minnesota Governor Tim Pawlenty was asked to explain his endorsement of a cap-and-trade anti-pollution plan for the Upper Midwestern United States. He said he made a mistake in backing it, pure and simple.
"Everybody's got a couple of clunkers in their record. That's one of mine. It was a mistake, I'm sorry. It was dumb," Pawlenty said.
Obama has hit a rough patch in the polls over high gasoline prices and concerns over the economy, but the Democrat remains a formidable candidate for re-election. Many Democrats believe he is benefiting from the slow start to the Republican race.
Minnesota Representative Michele Bachmann, a favorite of the conservative Tea Party movement, said sweeping cuts in government spending were needed to limit government's reach.
Referring to Obama's healthcare plan, Bachmann said if Republicans did not have the votes in Congress to repeal it, they should use their power to deny funding for it.
"If we can't repeal it, we should not spend one dime to put this Frankenstein in place," she said.
Former Senator Rick Santorum and businessman Herman Cain also spoke at the event and voiced concern about America's fiscal situation and the need to generate more job growth.
The gathering demonstrated there was no clear front-runner for the Republican nomination, although Romney, who ran for the nomination in 2008, is arguably the leading figure and topped Obama in a poll of New Hampshire voters.
"Somebody's going to rise, tough to know who, but I like what I heard tonight from all of them," said New Hampshire state Republican Party chairman Jack Kimball. (Editing by Peter Cooney)