IF JOHN MCCAIN hopes to win the key state of Pennsylvania, conventional wisdom holds, he'll have to find his votes outside Philadelphia, which is teeming with devoted African-American supporters of Barack Obama.

But those offering that wisdom should make a trip to Mayfair.

It's a white working-class neighborhood of attached brick houses and modest commercial strips in Northeast Philadelphia, where Republicans aren't an endangered species, Democrats can swing any which way and Obama has his work cut out for him.

No Republican expects McCain to win Philadelphia, but if he and running mate Sarah Palin can hold Obama's margin in the city to 350,000 votes or less, GOP insiders think that they could win the state and its 21 electoral votes.

That's why Republicans are looking carefully at Mayfair and the rest of the Northeast.

"I'm pulling out all my guns in Philly to make sure John McCain can win Pennsylvania," said Rob Gleason, state GOP chairman.

McCain's campaign has set up its city headquarters in Mayfair, at Frankford and Cottman avenues. And McCain made a Northeast stop yesterday, serving coffee and doughnuts to firefighters at a fire station in Fox Chase.

Four years ago, Sen. John Kerry beat President Bush in every ward in the Northeast. In the 55th Ward, which covers Mayfair, his margin was 15 points. But this year's presidential matchup is different, and Republicans are encouraged by what they saw in the April Democratic primary.

Democrats in the Northeast overwhelmingly backed Sen. Hillary Clinton. Clinton was cheered by an adoring crowd of 1,500 at a rally held outside the Mayfair Diner, and she went on to crush Obama in the Northeast, winning the 55th Ward with 75 percent of the vote. So far, her voters have not all converted to Obama.

When you add skeptical Democrats to the 72,000 registered Republicans in the Northeast, you've got a real shot for McCain to shrink Obama's margin in the city Obama needs to win big.

"I already made my mind up and I'm a Democrat - McCain," said Diana Linke, 49, of Mayfair, who supported Clinton. "I don't believe Barack Obama has the experience."

Democrats have said that Obama needs to win Philly by more than 400,000 to win Pennsylvania.

Kerry secured a 412,000-vote margin in Philadelphia in 2004 and went on to win the state. But McCain's Northeast support could impact that margin.

"I think McCain will do well up there," said political analyst Larry Ceisler. "The problem in some of these places, Obama's message is change, and people in these places don't want a change."

The Republicans struggled in the Northeast four years ago because President Bush was widely disliked. But McCain is favorably viewed as an experienced, independent senator. And, just as in other blue-collar areas, these working-class voters who are worried about gas prices, health-care costs and jobs haven't warmed to Obama.

"I'm voting for McCain because Obama is all b.s.," said Democrat George Scaricamazza, 67, of Somerton, who voted for Clinton in the primary. "He's not qualified for nothing."

Obama's Pennsylvania spokesman, Sean Smith, said that the campaign must educate voters in Northeast Philadelphia about Obama.

"We need to tell his story and let voters know that Senator Obama's early life was a lot more like their own than they may realize," Smith said.

The Obama campaign also needs to talk with Northeast voters about economic issues, Smith said.

"The Democrats who voted for Senator Clinton were doing so because of the economy and because of health care," said Smith. "We believe they will vote for Senator Obama on those issues because he is so much better than John McCain."

The selection of Scranton-born Sen. Joe Biden, a Catholic with blue-collar roots, may help Obama in this part of the city.

"I'm going to vote for Obama and Biden," said Emily Deane, 52, of Crescentville, who supported Clinton in the primary. "Biden has experience; he's been in the Senate for 30 years. Biden made up my mind."

But McCain's running mate, Alaska Gov. Sarah Palin, a self-described "hockey mom" with five kids, could also appeal to Northeast voters.

"I think she's going to be a great addition to the ticket," said Gleason. "I think she's a woman who understands a lot of the issues of being a working mom."

Another element of both sides' strategic thinking is the Northeast's, (and the city's) history of racial identification in voting. In 2003, the 55th Ward voted for white Republican Sam Katz over Mayor John Street, who is black, by an almost 9-to-1 ratio.

The Northeast also voted for white candidates Tom Knox and Bob Brady in the 2007 mayoral primary, though African-American candidates got a larger share of the Northeast's vote than in previous mayoral contests.

"I think, obviously, race plays a part of this," said Gleason. "But in America, you can vote for somebody on how they part their hair."

Annette Blumenthal, 47, of Pennypack, said she would support McCain over Obama, in part because of race.

"He's a smart guy, he's looks very educated, he has a beautiful wife," she said of Obama. "I just think the world's not ready for a black president." *