"Gov. Romney has extremely limited experience in that area, to say the least," McCain said about the wars in Iraq and Afghanistan and the threat posed by radical Islamic extremists.

Speaking with reporters aboard his Straight Talk Express bus en route from downtown Detroit to a town hall meeting in Howell, McCain said that he has the credentials to keep the country safe.

"I've been involved in every major national security issue for the last 20 years, and in some ways the last 40," said McCain, who has been in Congress since 1982 and spent more than five years as a prisoner of war during the Vietnam War.

"I have been an agent of change the greatest agent of change is one who saves American lives," said McCain, who last year bolted from his own party and said the Rumsfeld strategy was failing in Iraq.

McCain called for a surge in troop strength, a plan President Bush adopted and at least for now seems to be achieving the intended results.

McCain also said Romney, the former Massachusetts governor and Michigan native, was wrong to say that he supported a phased withdrawal of U.S. troops from Iraq.

"That's the worst kind of change, because it would have put many American lives in harm's way.

Sarah Pompei, a spokesman for Romney, said McCain is wrong. She said Romney never called for a phased troop withdrawl. Romney, she said, has said success by U.S. forces could allow the United States to draw down troops and turn over security to the Iraqis.

On another issue, McCain defended his campaign's sending out of flyers which said "if Michigan Republicans thought (Democratic Gov. Jennifer) Granholm was bad, Romney is worse."

"He raised taxes by $700 million and called them fees in Massachusetts," McCain said of Romney.

He also said that Romney in 2002 suggested a tax on SUVs, which were the bread and butter of the U.S. auto industry.

"I don't know of any jobs he created and I don't think he helped the American auto industry when he proposed the tax on SUVs, something I would never do," McCain said.

McCain is in the second day of a four-day swing through Michigan. Polls show he and Romney locked in a close struggle with former Arkansas Gov. Mike Huckabee also a big factor in the race.