WASHINGTON – Republican presidential candidate John McCain conceded battleground Michigan to Democrat Barack Obama on Thursday, a major retreat as he struggles to regain his footing in a campaign increasingly dominated by economic issues.

McCain’s campaign confirmed it was pulling staff and advertising out of the economically distressed Midwestern state. Resources will be sent to competitive states including Maine, where the campaign checked advertising rates this week.

“We are opening up an aggressive front in Maine, where we have strong numbers and where they split their electoral votes,” Mike DuHaime, political director of the campaign, said in a conference call with reporters.

Maine is one of only two states – Nebraska being the other – that award their electoral votes by congressional district. In Maine, two votes go to the overall winner, and one vote goes to the winner of each district.

In other states, the winner takes all of the electoral votes.

John Kerry took Maine’s four electoral votes in 2004, winning in both of the state’s congressional districts. Kerry won handily in the 1st Congressional District with 55 percent of the vote. The 2nd District was closer, with Kerry winning 52 percent of the vote.

A SurveyUSA poll taken last week showed Obama ahead in Maine 49 percent to 44 percent. Obama carried both congressional districts by 5 percentage points, according to the survey.

That poll, although showing Obama ahead, also showed the race to be tightening, according to local McCain supporters.

Cary Weston, chairman of the Bangor Republican Committee, said McCain’s new focus on the state would help their local effort.

“Day after day, the volunteers talk about it, you knock on doors, hand out fliers, and there’s no instant gratification, no immediate emotional return on your investment,” he said.

“But when something happens to let you know the big picture has noticed, and you’re in play because of those little things, it rejuvenates people. That one door-knocker may be the tipping point.”

The Obama campaign has been knocking on doors, too.

Toby McGrath, director of Obama’s Maine campaign, said it has built a strong ground operation and is registering new voters in the state.

“We will be working hard to earn each and every vote,” he said.

McCain’s decision to leave Michigan marked the first time either he or his Democratic rival has tacitly conceded a traditional battleground state in a race for the White House with little more than a month remaining.

In a campaign now unfolding across more than a dozen states, the decision means Obama can shift money to other states like Virginia, Colorado and North Carolina where he is trying to eat into traditional Republican territory. Besides Maine, McCain’s resources were being sent to Ohio, Wisconsin, Pennsylvania, Florida and other more competitive states.

By pulling out of vote-rich Michigan, McCain conceded a large part of the electoral map in the heart of the industrial Midwest.

The move underscored McCain’s troubles on the economy, which he has acknowledged is not his strongest subject. It also underscored his struggle to beat an opponent who has the money to compete in many states President Bush won four years ago. Polls show Obama has pulled ahead or tied McCain in many of those states.

Obama rejected public financing so he can spend as much as he can raise; McCain’s direct spending is limited to $84 million in taxpayer money. But McCain is getting help from the Republican National Committee, which announced Thursday that it had raised nearly $66 million in September. The Democratic National Committee has not been as big a help for Obama, but his massive fundraising makes him rely less on the party.

As Nov. 4 approaches, both sides are adjusting their strategies daily to find the best state-by-state path to the 270 electoral votes needed for victory.

Obama already has abandoned efforts in Alaska, Georgia and North Dakota, but the Democrat has succeeded in making traditional Republican strongholds Indiana, North Carolina and Virginia competitive. Both sides are battling it out in those states, where public polls show Obama ahead or tied.

The two campaigns are squaring off with increasing intensity in Colorado, Ohio, Florida, Iowa, Missouri, Nevada, New Mexico, which Bush won in 2004, and Wisconsin, Pennsylvania and New Hampshire, which went to Kerry.

Obama also is making a limited effort in the traditional GOP bastion of Montana and McCain is going after Democratic-tilting Minnesota.

Said Obama campaign manager David Plouffe: “This is a meaningful moment strategically. Their narrow path just got narrower.”

McCain had identified Michigan early on as a potential target, particularly in light of Obama’s troubles with white working-class voters in other Rust Belt primaries although he skipped Michigan because of a Democratic Party fight over its primary date and didn’t set up a campaign organization there during the primary.

But Michigan posed other difficulties for McCain. It has a Democratic governor and the nation’s highest annual average unemployment rate since 2006. McCain’s 90 percent support in the Senate for the unpopular President Bush, a theme hammered by Obama, proved too much for the GOP nominee to overcome.

Republican strategists said those troubles became more acute for McCain in Michigan after the Wall Street collapse, and both public and private polls showed him sliding. On Wednesday night, the campaign decided that the $1 million a week it was spending in Michigan wasn’t worth it with internal polls showing Obama approaching a double-digit lead.

“It’s been the worst state of all the states that are in play and it’s an obvious one, from my perspective, to come off the list,” said Greg Strimple, a McCain senior adviser.

Word of McCain’s pullout came as the vice presidential candidates, Republican Sarah Palin and Democrat Joe Biden, prepared for an evening debate in St. Louis and just before Obama took the stage for a rally at Michigan State University, his third event in the state in five days.

If the Illinois senator knew about McCain’s plans, Obama didn’t mention it and continued to criticize his rival’s economic policies. “My opponents’ philosophy isn’t just wrongheaded, it reveals how out of touch he really is,” Obama told more than 15,000 gathered on a chilly fall afternoon.

McCain’s decision didn’t go over well with at least some Michigan Republicans.

“We want him in Michigan. We want him to hear our issues,” said Mike Bishop, the top-ranking Republican in the state Legislature.

BDN writer Jessica Bloch, Maite Jullian of the Boston University Washington News Service, and The Associated Press contributed to this report.