Continuing his relentless pursuit of a state in which he has long trailed in the polls, Sen. John McCain will return to the Pittsburgh region Tuesday for a rally in Moon.

The Republican nominee will address supporters on the campus of Robert Morris University in his third appearance in Pennsylvania in a week. He spoke at rallies in Montgomery County and Chester County in the days preceding and following his debate Wednesday night with Sen. Barack Obama. His running mate, Gov. Sarah Palin, was in Lancaster County yesterday while her husband, Todd Palin made several stops in Western Pennsylvania.

Mr. McCain has made a major push for the state's electoral vote, the biggest prize remaining among the states won by Sen. John F. Kerry four years ago that the Republican still considers winnable.

Mr. Obama held a series of rallies in Philadelphia on Oct. 11 and his wife, Michelle, was in Pittsburgh Thursday, but overall, the Republican candidate has made more that twice the number of appearances in the state than his rival since they each clinched their parties' nominations.

Mr. McCain outspent his opponent on Pennsylvania television advertising through the summer and early September. For the last month, however, his presence on the state's paid airwaves has been overwhelmed by the free-spending Democrat.

Mr. McCain has trailed in surveys of Allegheny County, but the surrounding communities of southwestern Pennsylvania represent one of his strongest areas in the state.

While counties such as Washington, Beaver and Westmoreland retain Democratic registration edges, they include many Democrats who are conservative on social issues and whose votes have gone to Republican candidates in national and statewide elections over the last decade.

Statewide, however, Mr. McCain faces a bigger challenge as recent polls have shown him laboring with a double-digit deficit to his Democratic rival. In the latest daily tracking poll conducted by Muhlenberg College, he trailed Mr. Obama, 52 percent to 39 percent -- a daunting margin that has barely budged over the last two weeks.

"What you're seeing with this visit is more of the commitment of time and energy from the campaign," said Peter Feldman, a spokesman for the McCain campaign. "It's indicative of our level of confidence in our ability to carry the state."

Mr. McCain was in North Carolina and Virginia yesterday, two normally Republican states in which Mr. Obama has surged to the front in recent weeks. Today, he is scheduled to appear in Toledo, Ohio, with America's new plumber-in-chief, Joe Wurzelbacher who, was elevated to instant icon status last Wednesday, through Mr. McCain's repeated references at the final presidential debate last week in New York.

No Republican has won the White House without winning Ohio, but it is another Bush-voting state that now appears to be leaning toward Mr. Obama.

The potential for losses in such traditional red states has increased the urgency for Mr. McCain to find a recently Democratic state, such as Pennsylvania, to switch to his column.

Mr. Obama was in one of those wobbling red states yesterday, as he addressed a huge audience, estimated at 100,000, gathered under the Gateway Arch in St. Louis.

Republican officials had yet to announce an exact time for the Tuesday rally, but doors will open at 3:30. Tickets for the event are being distributed by local GOP party offices.