Speaking before a group of doctors, health policy experts and local officials at the University of Michigan medical complex, he embraced the aspect of the Massachusetts law most criticized among Republicans, the mandate that individuals buy insurance. He said it was necessary, given the needs of his state at the time.

But Mr. Romney said that if he were president he would seek to repeal the new national health care law with its similar mandate, arguing that it was inappropriate for the federal government to prescribe such a sweeping measure for states.

"Our plan was a state solution to a state problem," he said while walking his audience through a corporate-style slide presentation, "and his was a power grab by the federal government to put in place a one-size-fits-all plan across the nation."