(Adds Democratic debate quotes, vote results)
By Andrew Stern
SOUTHFIELD, Mich., Jan 15 (Reuters) - Mitt Romney scored a breakthrough win over rival John McCain in Michigan on Tuesday, reviving his struggling campaign and scrambling a chaotic Republican presidential race with no clear front-runner.
Romney, a former Massachusetts governor, desperately needed a victory in the economically ailing midwestern state to keep his White House hopes alive after second-place finishes in the first two contests to find a Republican candidate for the November election.
“Tonight marks the beginning of a comeback, a comeback for America,” Romney told cheering supporters in Southfield, Michigan. “Tonight is a victory of optimism over Washington-style pessimism.”
While the Republican returns rolled in, Democratic White House contenders Barack Obama and Hillary Clinton promised in a friendly debate in Nevada -- site of that party’s next contest on Saturday -- they would end a harsh dispute over race that roiled the campaign in recent days.
“We both have exuberance and sometimes uncontrollable supporters,” said Clinton, a New York senator and former first lady. “We need to get this campaign where it should be. We’re all family in the Democratic Party.”
Romney’s Michigan victory heightened the intensity of the wide-open U.S. race to succeed President George W. Bush.
Three different Republicans have captured the first three significant contests -- McCain, an Arizona senator, took New Hampshire last week and former Arkansas Gov. Mike Huckabee won in Iowa on Jan. 3.
“For a minute in New Hampshire I thought the campaign might be getting easier,” McCain said in South Carolina, where he headed before the Michigan results were even tallied. “I think we’ve shown them we don’t mind a fight.”
With 89 percent of the vote counted in Michigan, Romney easily led McCain by 39 percent to 30 percent, with Huckabee in third at 16 percent.
The Republican race now moves to Nevada and South Carolina on Saturday, and then the Florida primary on Jan. 29, where former New York Mayor Rudy Giuliani, who won just 3 percent in Michigan, hopes to spring back into contention. After that come the Feb. 5 “Super Tuesday” contests in 22 states.
Huckabee also headed to South Carolina before Michigan’s results were known. Romney will join them there on Wednesday.
“It looks like I won Iowa, John McCain won New Hampshire, Mitt Romney won Michigan,” said Huckabee, an ordained Baptist minister who hopes to win support from South Carolina’s large bloc of evangelicals. “Ladies and gentlemen, we’re going to win South Carolina.”
Exit polls in Michigan showed Romney and Huckabee ran even among evangelicals, who were key to Huckabee’s win in Iowa.
Democrats also held a primary in Michigan but a dispute over the date led the national party to strip the state of its delegates to this summer’s presidential nominating convention, making the contest meaningless.
Obama and Edwards were not on the ballot and Clinton, the only top contender listed, rolled to an easy win over Ohio Rep. Dennis Kucinich, former Alaska Sen. Mike Gravel and a ballot listing for “uncommitted.”
The Republican race in Michigan, which suffers the highest unemployment rate of any U.S. state at 7.4 percent, nearly 3 points above the national average, pushed the economy to the top of the campaign agenda.
McCain promised lower taxes and reduced government spending would make the United States more competitive globally and create new jobs in the slumping auto industry, but he said those jobs that had been lost would not be coming back.
Romney called McCain a pessimist, stressing his background running the Salt Lake City Olympics and as a businessman. He said he would restore Detroit’s lost power by lifting the regulatory burden on companies and boosting research to generate new jobs.
Exit polls showed more than half of Michigan voters listed the economy as the top issue, and Romney led among those.
Romney also emphasized his family roots in Michigan. His father was a senior auto executive and popular governor in the 1960s.
McCain, who won the state during his failed 2000 presidential bid, hoped for a big turnout among independents and Democrats, who could vote in either primary. But exit polls showed only about a quarter of voters in the Republican race were independents.
The issue of race dominated the Democratic campaign for two days after Clinton accused Obama, who would be the first black U.S. president, of distorting her remarks that some interpreted as a slight to slain civil rights leader Martin Luther King.
The two Democrats, in a tight race in Nevada along with former North Carolina Sen. John Edwards, said their supporters had fanned the dispute but there were other issues to pursue.
"We can't solve these challenges unless we can come together as a people and we're not resorting to the same -- or falling into the same traps of division that we have in the past," said Obama, an Illinois senator. (Writing by John Whitesides; Editing by Doina Chiacu) (For more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)