Philadelphia region a key to Obama's win in Penna.

Sen. Barack Obama's victory in the key state of Pennsylvania was based on racking up a huge majority in Philadelphia, scoring big-time in the suburbs and doing enough to hold off Sen. John McCain in the rest of the state.

With its mix of major metropolitan areas, small towns and farming areas, Pennsylvania is as diverse as any state in the union. That, together with its hefty 21 electoral votes, made it one of the most sought-after prizes on Election Day.

The principal issue that benefited Obama here was the same as in many other states with an aging population and a declining industrial base.

"It was the economy," said Jack Treadway, a political science professor at Kutztown University. "The economy, without question, trumped everything else. And Obama had such a big advantage on that issue that he rode it to victory."

McCain staked everything on winning Pennsylvania - the biggest of the Democratic-leaning states that appeared attainable for him. Though he trailed in every independent poll for two months, he saw something in the state - its socially conservative, aging population, its hundreds of small towns - that made him believe an upset was possible.

Obama, feeling confident about the polls - and the tens of thousands of new Democrats he had helped enroll - seemed to want to focus elsewhere toward the end. He spent far less time in Pennsylvania than McCain. But he kept up the pressure with massive spending on TV ads and organizing his get-out-the-vote efforts from an unprecedented 81 campaign offices.

With votes still being counted late last night, Obama appeared to be headed toward a bigger state victory than Sen. John Kerry commanded in 2004. Kerry then beat President Bush by 51 percent to 48.5 percent, with some votes going to minor candidates.

Exit polls commissioned by the Associated Press and the major television networks showed that Obama had strong appeal among most groups of voters.

The exit polls showed him getting almost six in 10 votes among women. That might have been expected, since women generally favor Democrats. But Obama also got a majority of votes among men.

Obama won about six in 10 votes among independents, and ran up about 95 percent of the African American vote. In 2004, Kerry had done quite well to get 84 percent of the black vote.

Geographically, the key to Obama's victory was in the vast margin he built up in the Philadelphia region.

Republicans made a big effort to pick off white votes in about 17 of the city's 65 wards. But with votes still being counted, Obama appeared likely to have done even better than Kerry, who won the city by 412,000 votes.

Democratic analysts said Obama may have carried Philadelphia by a half-million votes.

"Outside of Philadelphia, it looks like a lot of areas are going to McCain," Democratic state chairman T. J. Rooney said late in the evening. "But with a major plurality like that in Philadelphia, it just negates what went on in some of the other counties."

Going into yesterday's vote, Democrats had won each of the four previous presidential elections in the state. But the results of the Kerry-Bush election and the 2000 contest between Bush and Vice President Al Gore were close.

Jim Hoefler, a political science professor at Dickinson College, said that given the state's close election history, McCain had no choice but to focus much of his effort on Pennsylvania.

"McCain saw that he was going to lose at least one or two red states, so he had to make that up someplace," Hoefler said yesterday.

Hoefler said McCain was encouraged by the fact that Sen. Hillary Rodham Clinton - casting herself as the champion of Pennsylvania's blue-collar voters - had trounced Obama in the state's April Democratic primary.

Clinton decisively won the white, working-class vote - a group Obama had irked by saying in San Francisco that small-town Pennsylvanians seemed to cope with economic hardship by clinging to their guns and religion.

Yesterday's exit polls showed that McCain won the favor of about one in five Democrats who had voted for Clinton. He needed more.

Most voters told the exit pollsters that race was not a factor in their decision. Voters who did say it was important were about evenly split between Obama and McCain.

If anything, Pennsylvania is more crucial for Democrats than it is for Republicans. The last time a Democrat won the presidency without taking Pennsylvania was 1948, when Harry Truman won.

And no Democratic nominee since Lyndon Johnson in 1964 has gotten more than 51 percent of all votes.

In the suburbs, incomplete returns last night showed Obama leading by sizeable margins in each of the four counties: Bucks, Chester, Delaware and Montgomery.

In 2004, Kerry had won three of the four counties, losing only Chester. By nominating a moderate widely perceived as a maverick, the Republicans had hoped to do better this time.

But since the last presidential election, the suburban landscape has changed. Four years ago, registered Republicans outnumbered Democrats and independents, combined, in every one of the suburban counties. But Democrats now hold a plurality in Bucks and Montgomery counties. Overall, the number of R's and D's is about equal across the suburbs.

Marcel Groen, Democratic chairman of Montgomery County, said that Obama appeared to do even better than Kerry in his county. He said that voter turnout may have been the heaviest in decades.

"Everything was better," Groen said.

Bob Asher, of Montgomery County, cochairman of the McCain campaign in Pennsylvania, said that "up until about six weeks ago" he was optimistic that McCain would win Pennsylvania.

"We really felt we were very much in the game," he said. "But then the economy went south. That was very difficult for us. It refocused the whole campaign more on the economy and President Bush."