The Obama campaign is fully aware of the challenge.

“This is a tough ward,” said Paul Rossi, 61, a data processor who lives in the neighborhood and is helping out at an Obama office that opened Saturday not far from Marconi Park. “It’s a matter of convincing people culturally that they won’t be harmed by Obama.”

It is no accident that Senator Joseph R. Biden Jr., Mr. Obama’s running mate, is being dispatched to speak in Marconi Park on Monday night for his final rally of the campaign. The white, blue-collar Catholics here are just the kind of voters whom Mr. Biden, also Catholic, was chosen to help win over. Mr. Biden is to be joined by members of the Philadelphia Phillies, who just won the World Series.

Susan Streicher, 59, a retired secretary and registered Democrat, acknowledged that Mr. Biden’s Catholicism was appealing to her but said she preferred Mr. McCain and Gov. Sarah Palin, Mr. McCain’s running mate, because they oppose abortion rights. Her husband, John, 63, a postal worker, dismissed Mr. McCain, saying that he was a “warmonger” and that Alaska, Ms. Palin’s home state, “is all wilderness.” Both said they thought Mr. Obama would win.

Several other people interviewed who said they preferred Mr. McCain declined to give their names.

There is no doubt that Mr. Obama, who won Philadelphia in the primary, will again sweep the city, where about 52 percent of voters are black. But while it is a major part of the statewide puzzle, it is still only a piece.

In 2004, Senator John Kerry, the Democrat, won about 80 percent of the vote in Philadelphia, beating President Bush by 412,000 votes here. But Mr. Kerry won the state by only 144,000 votes.

Gov. Edward G. Rendell of Pennsylvania said Sunday that although he still expected Mr. Obama to win the state, he was “nervous” and had been on the phone “screaming at Chicago,” meaning the Obama headquarters, to send reinforcements. Mrs. Clinton is due in Pittsburgh on Monday; former President Bill Clinton is to stump for Mr. Obama across the state the same day.

Mr. McCain continues to devote his most precious resource, his time, to Pennsylvania. He made three in-person pleas to voters in the eastern part of the state over the weekend and has planned a short rally for Monday at the Pittsburgh airport.