Republican Herman Cain faces harassment allegations by four women against

(Reuters) - Republican Herman Cain will try to move past an escalating sexual harassment controversy on Wednesday during a U.S. presidential debate on economic issues held in the hard-hit manufacturing state of Michigan.

The debate will be a homecoming for Cain's rival Mitt Romney, who was born in Michigan and hopes to consolidate his status as the candidate-to-beat in the Republican race to choose a 2012 challenger to President Barack Obama.

The economic focus is likely to limit discussion of the harassment allegations by four women against Cain, which threaten to derail the former pizza executive's White House campaign despite his denials.

But the controversy, which has lingered for more than a week, will be hard for voters to forget. Polls show it has eroded favorable voter perceptions of Cain without knocking him from his spot near the top of the pack with Romney so far.

"This debate is going to be about Herman Cain even if nothing is said about the harassment allegations all night," Republican strategist Ford O'Connell said.

Cain's rivals have tiptoed around the subject, trying to avoid looking like they are piling on. Romney and Newt Gingrich urged Cain on Tuesday to address the charges, which he did in a news conference where he repeated his denials and vowed they would not force him to withdraw.

Cain's difficulties could open the door for one of the handful of other candidates battling for the allegiance of conservatives in hopes of becoming the clear alternative to the more moderate Romney in the Republican race.

"The whole Cain saga creates a real opportunity for one of the other anti-Romney candidates, someone like Newt Gingrich or Rick Perry, to shine," O'Connell said.

So far conservatives have failed to coalesce around a single candidate. A series of conservative contenders -- first U.S. congresswoman Michele Bachmann, then Perry and now Cain -- has risen in polls to challenge Romney only to fall back.

GINGRICH ON THE RISE?

Gingrich, the former U.S. House speaker, has seen his poll numbers inch up and hopes to challenge for a spot in the top tier. Perry, the Texas governor, is still mired in the middle of the pack but has started to air campaign commercials in states with early nominating contests.

Support for Romney, the former Massachusetts governor, has held relatively steady in the mid-20s in polls for much of the year.

Eight candidates will participate in the 8 p.m. EST/0100 GMT debate at Oakland University in Rochester, Michigan, outside Detroit.

The economic struggles in the state, which has seen its manufacturing base hit hard by the economic downturn, will serve as a backdrop to the debate. The state unemployment rate of 11.1 percent in Michigan is the third-highest in the country and well above the 9 percent national rate.

Romney, whose father was a former Michigan governor and a former auto executive, is likely to be in the hot seat again as the rest of the Republican field races to catch up.

"Realistically, Romney is going to be a target, especially given the fact he is from Michigan and continues to be perceived as the guy to beat by a lot of folks," said Saul Anuzis, a former Michigan state party chairman and a Romney supporter.

Democrats got the ball rolling on Tuesday with an attack on Romney for opposing the 2009 auto industry bailout that helped revive Michigan-based General Motors and Chrysler. The web video featured a Romney column written in 2008 titled "Let Detroit Go Bankrupt."

Democrats hope the issue will be a potent one for Obama if he meets Romney in a 2012 general election match.

With the Republican campaign consumed for more than a week by the Cain scandal, Anuzis said he expected a concerted effort to focus on economic issues like the flat tax plans from Cain and Perry and to stay away from the Cain controversy.

"I think there will be pressure to ensure they stay on the issues and there is some substance to it," Anuzis said.