PHILADELPHIA (AP) — Older, whiter and more female than the nation as a whole, Pennsylvania looks like Hillary Rodham Clinton country. Wealthier, better educated and more African-American than the rest of the state, Pennsylvania’s thickly settled southeast corner could belong to Barack Obama.

For six weeks, the two Democratic presidential rivals have courted their political bases and sought to carve up each other’s support with an increasingly tart tone. After both deluged the state with ads, crisscrossed it on buses, planes and trains, and had a parade of surrogates march through it, Clinton holds a slight lead.

Pennsylvania’s primary Tuesday has the potential of being decisive, or it could extend a campaign that has gone far longer than most ever imagined.

Clinton, the New York senator, is looking to validate her case that only she can win big state primaries. Obama, the Illinois senator who leads in delegates and in the national popular vote, wants to shut Clinton down so he can turn his attention to the presumed Republican nominee, John McCain.

A defeat for Clinton here could be devastating. One of her key backers, New Jersey Gov. Jon Corzine, said last week that a Pennsylvania loss for her would be “pretty much a door closer.”

At stake are 158 delegates, with 103 apportioned by how each candidate fares in each of Pennsylvania’s 19 congressional districts. The remainder are distributed based on the statewide vote. The state has 29 superdelegates — party officials and elected officials who can support whomever they chose. Fifteen have endorsed Clinton and five have endorsed Obama.

Hillary Clinton, as the state’s old slogan used to say, has a friend in Pennsylvania. Its population of 12.4 million has a higher median age, a higher percentage of whites, a lower median household income and fewer bachelor’s degrees than the country overall. These are the voters — working-class whites and voters older than 50 — who have flocked to her in past contests.

Obama and his allies are counting on Philadelphia and the Philadelphia suburbs to be the underpinnings of his campaign. They also hope to do well in Pittsburgh. Philadelphia is 44 percent black and Pittsburgh is 26 percent black. Both are higher education hubs, with students and academics who tend to be Obama voters.

Clinton has drawn more conservative voters, whereas the two cities have Democrats who are more liberal than in the rest of the state. Moreover, Philadelphia’s surrounding counties also trend in favor of Obama with their greater number of upscale voters and college students.

“Southeast Pennsylvania will go for Obama,” said Robert Maranto, a political scientist at Villanova University. “There’s a huge black vote in Philadelphia. The suburbs are a lot more pro-Obama.

“The rest of the state should go pretty heavily for Clinton,” he added.

Obama’s support in Philadelphia was evident by a rally there Friday that drew 35,000 people, the largest crowd of his campaign. Yet Clinton has the backing of Gov. Ed Rendell, the city’s popular former mayor, and current Philadelphia Mayor Michael Nutter, one of the state’s prominent black leaders.

Obama, on the other hand, was endorsed by Sen. Bob Casey, a member of a prominent political family from the state’s more conservative northeast. Casey has spent considerable time at Obama’s side, traveling with him on his current train tour through the state.

Pennsylvania is the sixth largest state and the 41st to vote in this Democratic primary. It has about 4 million registered Democrats, thousands of them added in a recent registration surge. None of the remaining nine states is as big or as rich in delegates.

Between the two major cities are 7.7 million acres of farmland, with the kinds of small towns that harbor more conservative voters who, if not Republican, would be more likely to vote for Clinton. The state’s steel, coal and railroad industries have atrophied, contributing to the slowest population growth of any major state.