In the interview, Romney also took exception to rival John McCain's record on campaign finance and immigration policy, suggesting the Arizona senator's views have shifted as the 2008 presidential campaign has evolved.

"There are differences on issues and differences in experience," Romney said, reiterating earlier criticism. "The difference on issues between Senator McCain and myself are probably more clear because he's been out for a while and I've been out for a while."

Romney noted his hard-line stance on immigration and opposition to a campaign finance reform measure that McCain pushed with Sen. Russ Feingold, D-Wis.

"One of the biggest differences is McCain-Feingold," said Romney. "I think his campaign finance law was ill-considered and has been very harmful. That's a big difference."

And Romney described an immigration reform bill supported by McCain as "a badly crafted bill that would take us in the wrong direction on immigration."

McCain's proposal would let some illegal immigrants in the United States earn citizenship — a move Romney firmly opposes.

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Associated Press Writer Glen Johnson in Boston contributed to this report.