* 'Explanation not going to satisfy everybody'
* Democrats have praised Romney's Massachusetts law (Adds Wall Street Journal editorial, Santorum)
By Nick Carey
ANN ARBOR, Mich., May 12 (Reuters) - Republican Mitt Romney on Thursday played down the healthcare reforms he crafted as Massachusetts governor as he sought the support of conservatives for his party's 2012 presidential nomination.
The similarities between Romney's healthcare plan and that of Democratic President Barack Obama, derisively dubbed "Romneycare and Obamacare" by conservatives, are seen as the biggest challenge to Romney in his expected presidential bid.
"Our plan was a state solution to a state problem," Romney said in a speech at the University of Michigan's Cardiovascular Center in Ann Arbor. "While his (Obama's) plan is a power grab by the federal government to put a one-size-fits-all plan across the nation."
Romney is one of several Republican hopefuls dealing with issues from their past, which could further hinder a potential presidential field already seen as weak.
Former House of Representatives Speaker Newt Gingrich, who declared his candidacy on Wednesday, has sought to ease concerns among social conservatives about his extramarital affair in the 1990s.
Another possible candidate, Jon Huntsman, has had to deal with questions about why he served Obama's administration as ambassador to China until last month.
Former Minnesota Governor Tim Pawlenty has apologized for his past support of a cap-and-trade system on greenhouse gas emissions.
Democrats frequently praise the Massachusetts health system as the forerunner to Obama's reforms. Both include a mandate that nearly everyone should obtain health insurance.
Conservatives despise Obama's healthcare plan and want Congress to repeal it. It is that constituency Romney, an unsuccessful candidate for the 2008 Republican nomination, needs to win over.
"I know that this explanation is not going to satisfy everybody," Romney said. "And I respect the views of those who thought we took the wrong course."
Romney's position drew fire in a Wall Street Journal editorial on Thursday headlined: "Obama's Running Mate."
"The debate over ObamaCare and the larger entitlement state may be the central question of the 2012 election," the editorial said. "On that question, Mr. Romney is compromised and not credible. If he does not change his message, he might as well try to knock off (Vice President) Joe Biden and get on the Obama ticket."
Potential Republican presidential rival Rick Santorum also weighed in, saying, "Romneycare has, in fact, not made healthcare better or saved costs in Massachusetts.
"It's done just the opposite," Santorum said in a statement. "This is not a failure of execution, but a lack of foresight on Governor Romney's part to understand the implications of his policy proposals."
After briefly being eclipsed by real estate tycoon and celebrity TV star Donald Trump as front-runner of a large pack of potential Republican candidates, Romney topped a May 4 Quinnipiac University poll with 18 percent among Republican and independent Republican-leaning voters.
But he was only a few points ahead of former Alaska Governor Sarah Palin and former Arkansas Governor Mike Huckabee, who both scored 15 percent.
Romney's opponents are also expected to find fault with his career as a corporate raider in the 1980s and a mixed performance on employment when governor from 2003 to 2007.
As part of what appears to be a concerted effort to tackle criticism of his record head-on, Romney previewed his reform proposals in USA Today, promising his first act if elected president would be to overturn Obama's reforms. (Editing by Peter Cooney)