HANOVER, N.H. — Mitt Romney offered a robust defense of the health care plan he signed as governor of Massachusetts and sought to look beyond his Republican presidential rivals at a debate here Tuesday night by presenting himself as the leader who is best prepared to take on President Obama.

With a fresh air of confidence in his candidacy, Mr. Romney set out to diminish Gov. Rick Perry of Texas and all but ignored him, a different approach from the last three debates, where he repeatedly tangled with Mr. Perry. Given a chance to question a fellow candidate, Mr. Romney selected Representative Michele Bachmann of Minnesota.

In a debate that focused on the nation’s economic burdens, Mr. Romney defended elements of the Wall Street bailout in late 2008 as an imperfect but necessary solution. The view is at odds with the sentiment of many conservative voters, who will help decide the party’s nominee.

“My experience tells me that we were on the precipice and we could have had a complete meltdown of our entire financial system, wiping out all the savings of the American people,” Mr. Romney said. “So action had to be taken.”