He pledged to make restoring the domestic auto industry - once the linchpin of Michigan's economy - a top priority if elected president.
"In some respects, Michigan is like the canary in the mine shaft: What Michigan is experiencing, the whole nation will experience unless we fix what's happening in Michigan and learn lessons here we can apply across the nation," he said in Traverse City amid a fly-around of the state.
Romney's criticism of Washington was a none-too-subtle shot at McCain, an Arizona senator who has said that some of Michigan's lost jobs are gone forever. A Detroit News poll being released Sunday showed the race a statistical dead heat, with McCain at 27 percent and Romney at 26 percent. Huckabee was third with 19 percent.
McCain defended his comment during a raucous rally before 400 supporters in Warren.
"I had to give some straight talk," McCain said. "Jobs are leaving the state of Michigan. They have left and will not come back, but we're going to create jobs, we're going to create a new economy. This is the smartest technological place in America. We have the smartest people here. We can do it. We can create jobs here."
Later, aboard his campaign bus, McCain continued his criticism of Romney.
"Governor Romney says he supports the industry yet when he was running for the governor of another state he wanted to raise the tax on SUVs," McCain said.
Aides distributed campaign literature from Romney's 2002 race for governor in Massachusetts in which Romney proposed a 10-year sales tax moratorium on hybrid vehicles, as well as reworking the vehicle excise tax to encourage the purchase of fuel-efficient cars.
McCain also mentioned a Detroit News headline Saturday: "Experts Back Up McCain's Jobs Claim."
Romney, sitting later in the home of an unemployed woman in Marshall, responded by criticizing McCain for supporting an increase in fuel-efficiency standards, something Michigan automakers have resisted.
"I was the governor of Massachusetts, and Massachusetts is not the state that is propelling the Michigan economy," he said.
"Senator McCain was a U.S. senator, who has responsibility for the well-being of the entire country. ... Senator McCain has watched as Michigan has suffered."
Economics were a focal point because Michigan's unemployment rate, at 7.4 percent in November, is a full percentage point higher than any other state. It also is about 50 percent higher than the national average.
Bureau of Labor Statistics figures show the state shed more than 76,000 jobs in the 12 months ending in November, a period in which the national economy added 1.5 million jobs.
Huckabee's alternate focus on social issues highlighted his effort to reinvigorate the coalition of religious voters that propelled him to victory in Iowa.
The former Southern Baptist minister emphasized his opposition to abortion as he urged about 100 pastors in Grand Rapids to support him and use their address books and e-mail lists to mobilize others.
"I don't presume that you will support me because of a common faith," Huckabee told them. "I know that I have to earn that. But I also recognize this is a unique opportunity. For a long time, those of us who are people of faith have been asked to support a candidate who would talk to us. But rarely has there been one who comes from us."
He added, "Life is in the balance."
Comparing abortion to slavery, Huckabee also said that overturning the Roe v. Wade decision legalizing abortion would merely allow states to decide whether to value one life or another and called for a constitutional amendment banning the practice. He also played up his opposition to gay marriage, saying that traditional marriage helps "train our replacements."
While only 34 delegates were up for grabs in Michigan Tuesday, the candidate activity highlighted the state's importance in the battle for momentum.
McCain is hoping to build on his New Hampshire victory.
Huckabee, the former governor of Arkansas, is trying to recapture energy heading into next week's South Carolina primary. He decamped from Michigan to attend church Sunday in South Carolina, but he changed his schedule to return to Michigan Sunday afternoon and remain until Tuesday, seeking a surprise finish.
Romney, the former governor of Massachusetts, is seeking a first-place finish after his earlier second-place finishes prompted questions about whether he has hit a ceiling of support. Michigan is especially important: Romney grew up here and his father, George, was a three-term governor in the 1960s.
Former New York mayor Rudy Giuliani, who was campaigning in Florida Saturday, has ceded Michigan to the others. Former Tennessee Sen. Fred Thompson, campaigning in South Carolina, played on his expertise as a talk radio host before an overflowing crowd at a pancake house in North Charleston.
--- Associated Press Writers Liz Sidoti and Libby Quaid contributed to this report.
