HARRISBURG, Pa. (AP) _ Gov. Ed Rendell urged voters to "hang in there" if they faced long lines today as state and county officials braced for an expected huge turnout for a presidential race in which Pennsylvania was front and center.

Hoping to become the first Republican in 20 years to carry Pennsylvania, John McCain was back in the state Monday for a visit to Pittsburgh, his 25th day in the state since early June. Democratic vice presidential candidate Joe Biden headed to Philadelphia for a final campaign stop.

Barack Obama — who visited the state nine times during the same period — also got an assist from former President Bill Clinton, as well as hip-hop artists Jay-Z, Sean "Diddy" Combs and Mary J Blige, who appeared in Philadelphia for an Obama get-out-the-vote event. Pre-election polls consistently showed Obama in the lead.

McCain got last-minute help from former Massachusetts Gov. Mitt Romney and former New York mayor Rudy Giuliani.

Statewide contests were on tap for attorney general, treasurer and auditor general.

Competitive races were expected for at least three seats in the U.S. House of Representatives and a few dozens seats in the Pennsylvania General Assembly.

An estimated 6 million Pennsylvanians were expected to vote today, or 65 percent of residents old enough to vote.

Some political experts said turnout could exceed the record in 1960, when 70 percent of eligible Pennsylvanians cast ballots in the election won by John F. Kennedy, more than a decade before 18-year-olds won the right to vote.

McCain was looking for support from Republican strongholds in the central and northern regions, as well as crossover votes from working-class Democrats in the western and northeastern areas who helped Sen. Hillary Rodham Clinton defeat Obama in the April primary.

Obama was banking on a strong showing in Philadelphia, its suburbs and other areas Democratic nominee John Kerry won in 2004.

This year, Democrats added nearly 600,000 Pennsylvania voters to their rolls while the GOP lost a little ground. Democrats now outnumber Republicans by more than 1 million.

The governor said Pennsylvania's voting system was designed for turnouts of 60 percent to 65 percent but that turnout in some places could be as high as 80 percent.

"This is an important election," he said. "If you have to stand in line ... hang in there."

In other statewide balloting, state Attorney General Tom Corbett, a Republican, and Auditor General Jack Wagner, a Democrat, both faced challenges in their bids for second four-year terms.

Corbett was opposed by Democratic nominee John Morganelli, the Northampton County district attorney, and Libertarian Party candidate Marakay Rogers, a York lawyer.

Wagner, a Democrat, was opposed by Republican Chet Beiler, a Lancaster County businessman running for public office for the first time, and Libertarian nominee Betsy Summers, a Wilkes-Barre businesswoman.

The race for the open treasurer's seat pitted venture capitalist Rob McCord, a Democrat, against bond lawyer Tom Ellis, a Republican. The Libertarian nominee was Berlie Etzel, a retired professor from Clarion County.

In congressional races, three longtime Pennsylvania incumbents from blue-collar districts were fighting for re-election.

Rep. Paul Kanjorski, a 12-term Democrat from northeastern Pennsylvania, faced a GOP rising star in Hazleton Mayor Lou Barletta, who has made a national name in his opposition to illegal immigration.

At the other end of the state, in northwestern Pennsylvania, Rep. Phil English, a seven-term Republican, was challenged by Kathy Dahlkemper, an anti-abortion Democrat and business owner.

Also in western Pennsylvania, powerful House Democrat John Murtha, a 17-term member, was in a tougher-than-expected race after making controversial comments about his constituents.

Murtha described western Pennsylvania as racist, apologized for the remark, then told another interviewer the area had been "really redneck" in years past. He's challenged by William Russell, a retired Army lieutenant colonel who moved to the district to run against Murtha.

In the state House of Representatives, Republicans were hoping to regain control while Democrats sought to expand the 102-101 majority they won in 2006. The Democratic caucus was so fractured after the last election that it was forced to accept a Republican as House speaker.

Control of the Senate was not in question.

Also on Tuesday's statewide ballot was a single referendum question seeking voter approval for a $400 million bond issue to help pay for repairs to local water and sewer systems.