PHILADELPHIA -- Shorn of the inevitability that once illuminated her candidacy, Hillary Clinton last night won the Pennsylvania Primary -- its major prize, the chance to fight on.

"Today here in Pennsylvania you made your voices heard, and because of you, the tide is turning," Mrs. Clinton told a roaring crowd of supporters,

"We were up against a formidable opponent who outspent us three-to-one. He broke every spending record in the state. He tried to knock us out of the race. Well, the people of Pennsylvania had other ideas."

Mrs. Clinton promised a renewed push and even made a plea from the podium for donors to sign on to her cash-strapped campaign.

She was joined on stage by her husband, former President Bill Clinton, her daughter, Chelsea, and Gov. Ed Rendell, who jokingly chided Scranton Mayor Chris Doherty for turning out only 78 percent of the vote in Lackawanna County for Mrs. Clinton.

It could have ended here. Had Sen. Barack Obama scored an upset, a new surge of worry would have arisen about her viability. Last night, with the nominating race likely to stretch into summer, some of her top aides sketched out Plan B for their candidate.

One major task: matching Mr. Obama in the popular vote.

"She needs to be very near, equal or ahead in popular vote," said U.S. Rep. Joe Sestak, D-Delaware County, a key Clinton backer in this state.

Mr. Sestak said Mrs. Clinton could bring herself close with a series of wins or near-wins in the remaining nine primary contests.

"She's up in one poll in Kentucky, with 60 percent. If she wins that -- Kentucky and West Virginia -- and she balances North Carolina ... and she balances out in Indiana, those states and Puerto Rico and a real fight in Oregon, you begin to have numbers in the popular vote that edge up to even with Sen. Obama," Mr. Sestak said. "If that's the case, then you have legitimacy."

Clinton aides spent much of yesterday low-balling their estimates of her performance and suggested that an Obama loss, however narrow, revealed an underlying weakness in his candidacy.

"Sen. Obama has outspent us three-to-one here. I think people are going to start asking questions about his campaign, why he can't close the deal," said Mo Elleithee, a senior Clinton spokesman.

He described Pennsylvania as an important juncture in the Clinton effort, calling the debate last week a "huge" factor in slowing Mr. Obama's momentum.

He predicted that neither candidate was likely to have the delegates needed for the nomination by the final state primary vote June 3, opening the contest to the so-called super delegates -- elected officials and party leaders who have a vote on the nomination but are not bound by popular vote results.

"Neither candidate is going to have enough delegates to win the nomination even after all the states have voted. It's a mathematical impossibility for either candidate to do so," said Terry McAuliffe, former DNC chairman and a Clinton backer who said he has already begun a round of telephone calls to lobby that group.

But he predicted that the superdelegates will likely have decided.

"They want to be part of the primary process, they're going to make up their minds," he said.

One of those superdelegates, New Jersey Gov. John Corzine, said last night he believes Mrs. Clinton must now amass some impressive wins.

"I'm hearing from the campaign they feel like they have to win Indiana, have to have large margin victories in several of the remaining states," he said.

But one of the major tasks ahead involves sorting out the thorny issue of votes in Michigan and Florida.

Both states pushed their primaries ahead of the permitted schedule and the Democratic National Committee responded by declaring that their delegations would not be seated.

Democratic candidates agreed not to campaign in either state.

Mrs. Clinton handily carried the votes in both states -- Mr. Obama was not on the ballot in Michigan -- and her campaign is now arguing that those delegations should be seated.

Mr. Corzine said the delegation from Florida, at the least, should be seated at the convention.

"It was a fair fight, both people were on the ballot, neither one of them campaigned and there was a 300,000-vote majority there," he said.

At the Park Hyatt Philadelphia at the Bellevue, one of this city's storied hotels, more than 1,000 backers crowded into a ballroom. Roar after roar filled the hallways as networks projected a Clinton win. Red, white and blue confetti shot from air cannons filled the air.

For some, just getting into the building was a major task.

Linda Chabot and Teresa Fitzsimmons came here from out-of-state -- Ms. Chabot from Connecticut, Ms. Fitzsimmons from Florida -- to canvass the suburbs for the Clinton campaign.

Last night, they had to sneak in a side entrance in search of a place to cheer their candidate.

They had already made their way through a downtown street on which Obama and Clinton supporters, each toting signs, each howling to passing traffic, faced off and howled at each other.

The women skipped that one. But the sometimes sulfurous tenor of the campaign left them doubtful not about whether they would vote as Democrats in November, but whether they would do so enthusiastically if their candidate isn't the winner.

Ms. Chabot changed her registration to join the campaign.

"If she doesn't win the nomination I'm going to go back to independent and then I'm going to have to think about who I'm going to vote for," said Ms. Chabot.

"I think both of them have a lot of strong support," said Ms. Fitzsimmons. But it doesn't mean she would knock on doors in Philadelphia for Mr. Obama.

"I'm not going to work for him," she said. "I'm just not that impressed with him."