Pennsylvania Democrats threw a much-needed lifeline to Sen. Hillary Rodham Clinton yesterday, offering a fresh incentive to keep pursuing her dimming hopes of winning the party's presidential nomination and turning the May 6 primaries in Indiana and North Carolina into critical showdowns against Sen. Barack Obama.

Clinton's path to the nomination remains treacherous even after the victory in Pennsylvania. Her margin was decisive, but even some of her most loyal supporters privately expressed doubts last night that she can prevail in the long battle against Obama.

The senator from Illinois still leads in the number of pledged delegates and the popular vote. He is almost certain to hold the delegate lead and will probably maintain the popular-vote advantage when the primaries end in early June.

Perhaps more important, Clinton's campaign is nearly broke, while Obama has an enormous amount of money in the bank to throw into the next two contests and beyond.

But for the second time in seven weeks, first in the Texas and Ohio primaries and now in Pennsylvania, Obama failed to deliver a decisive blow against Clinton when he had an opportunity to bring the race to an end, despite heavily outspending her and waging an aggressive and negative campaign in the final days. His advisers had hoped to hold Clinton's victory margin to mid-single digits and appeared to have fallen short of that goal.

"He broke every spending record in this state trying to knock us out of this race," Clinton told her supporters in Philadelphia last night. "Well, the people of Pennsylvania had other ideas."

Clinton won at least 52 delegates to the party's national convention, with 60 still to be awarded. Obama won at least 46, according to an analysis of election returns by The Associated Press.

With 99 percent of precincts reporting, Clinton led with 55 percent, or 1,258,245 votes, to Obama's 45 percent, or 1,042,297 votes, according to AP.

The final delegate count isn't expected until today at the earliest because many of Pennsylvania's counties are split into multiple congressional districts. Election officials were working late last night to assign votes from split counties to the appropriate congressional districts.

In the overall race for the nomination, Obama led with 1,694.5 delegates, including separately chosen party and elected officials known as superdelegates. Clinton had 1,561.5 delegates, according to the AP tally. It will take 2,025 delegates to secure the Democratic nomination.

QUESTIONS FOR OBAMA

Obama's loss in Pennsylvania raised anew questions about his ability to win the big industrial states that will be critical to the Democrats' hopes of winning back the White House in November. In coming days, the Clinton camp will try to play on those doubts with uncommitted superdelegates, who have been moving toward Obama over the past two months, urging them to remain neutral until all the primaries are over.

Geoff Garin, Clinton's co-chief strategist, called Pennsylvania a potential turning point in the Democratic race.

"Sen. Obama had every opportunity to go out and make his case and show he could win an industrial state," he said. "The fact that Hillary not just held her own but gained strength at the end gives us real momentum going into Indiana and North Carolina."

But David Plouffe, Obama's campaign manager, said the loss was expected and did little to change the trajectory of a nomination battle that continues to favor his candidate.

"Some states are stronger for our opponent," he said. "Some are stronger for us. We assumed she had an edge there (in Pennsylvania) and we would try to keep it as close as we could. You have to be clear-eyed about that. We have two contests coming up in two weeks. We'll see where the race is after that ... The structure of the delegate contest will not be changed appreciably and that's the most important factor in the race."

By those calculations, Clinton faces an almost insurmountable hurdle.

Obama's team expects to recoup any loss of delegates in Pennsylvania with the results in North Carolina and Indiana. After those, just six contests will remain and the chances of Clinton winning enough of the remaining delegates to overtake Obama appears out of the question. Even her hope of taking a lead in the popular vote appears out of reach, given that Michigan and Florida will not be counted in the calculations because they violated Democratic Party rules in holding their primaries.

"We don't think this is just going to be about some numerical metric," Garin said. "When we get to those days after June 3, we think the real choice is who's proven themselves to be the best candidate."

That leaves Clinton with few options other than to keep winning as many of the remaining contests as possible and then pleading with superdelegates to set aside the numerical indicators of who leads and consider who would make the stronger nominee against Sen. John McCain of Arizona, the presumptive Republican nominee.

Clinton expects victories in West Virginia, Kentucky and Puerto Rico. Obama's team expects to win Oregon, North Carolina, Montana, South Dakota and Guam. That makes Indiana the critical battleground. Obama was there last night and Clinton will arrive today.

CLINTON STILL UNDERDOG

Clinton's victory in Pennsylvania came after a turbulent month in the Obama campaign. He was rocked first by controversy over incendiary statements from his former pastor, the Rev. Jeremiah Wright. Then came Obama's description of small-town voters as bitter over their economic situation, which he said leads them to "cling" to religion and guns.

After his loss in Ohio, Obama looked to demonstrate that he could attract more support among white, working class voters. But exit polls from Pennsylvania showed he made scant progress, despite a bus tour that took him from one end of the Keystone State to the other with an appeal designed to reach out to those voters.

One clear bright spot for Obama was the nearly one in 10 voters in the Democratic primary who had recently registered with the party. Pennsylvania saw a huge shift in voter registration over the last year, with Democratic registration rising by more than 300,000 and Republican registration shrinking by about 70,000. Among those newly registered Democrats who turned out yesterday, Obama won them by about 20 percentage points. His advisers will point to that as evidence that he can draw support from one-time independents or even disaffected Republicans in a general election race against McCain.

Clinton faces another significant handicap as she tries to block Obama's route to the nomination. Her negative ratings have risen enough in the past two months that she runs a great risk if she tries to defeat him by attacking him.

In almost every way, Clinton remains a distinct underdog in the Democratic race. But the results from Pennsylvania mean she will continue to fight on.

The Associated Press contributed to this report.