Pennsylvania votes in Democratic primary

WASHINGTON (Reuters) - Hillary Clinton sought a convincing win to keep her flickering White House hopes alive on Tuesday as Pennsylvania Democrats chose between her and Barack Obama in their presidential nominating contest.

Polls close at 8 p.m. EDT with results expected shortly thereafter.

Clinton, a New York senator, is favored in Pennsylvania but needs a substantial victory to gain ground on Obama in the Democratic nomination race and convince party leaders she is the best candidate to face Republican John McCain in November's presidential election.

Her one-time 20-point lead in the state has slipped to single digits in many polls amid an onslaught of advertisements by Obama, who has heavily outspent her in the first nominating contest in six weeks. Both camps tried to play down expectations before the vote.

"This was always an uphill climb but what we feel is that we've made significant progress," Obama said at a diner in Pittsburgh. "A lot of it is going to depend on turnout today and it's really hard to gauge."

Turnout was heavy at many polling places, local media said. A record number of Pennsylvanians are registered to vote in the state's first contested Democratic primary since 1976 and one poll showed most new registrants plan to vote for Obama.

The Pennsylvania vote opens the final phase of the Democrats' hard-fought duel for the nomination. Nine more contests are scheduled before the campaign ends on June 3.

PARTY LEADERS COULD DECIDE NOMINEE

Obama has a nearly insurmountable lead in popular votes won during the first three months of the primary battle and in delegates who will choose the nominee at the August convention. But neither can clinch the nomination without the help of superdelegates -- nearly 800 party insiders who are free to support either candidate.

Clinton hopes a big win in Pennsylvania ignites a strong run through the last nine contests, convincing superdelegates she is the candidate who can capture the big states that will be crucial in November.

"I think maybe the question ought to be: Why can't he close the deal? With his extraordinary financial advantage, why can't he win a state like this one, if that's the way it turns out?" Clinton told reporters in Conshohocken, a Philadelphia suburb.

A narrow Clinton win would probably keep her in the race but could prompt calls among Democrats for her to step aside and let Obama focus on the race with McCain. Clinton has already rallied from the brink of elimination twice in the state-by-state nominating process that started in January.

"I do believe we're coming to the end of this process," Obama said in Philadelphia, citing his lead in the delegate count and popular vote and the number of states he has won. Obama said he was still on track to win the nomination.

Clinton supporters said she should stay in the race until the August convention even if she loses Pennsylvania.

"I think she should go all the way to the end. I don't think she should drop out at all," said Anita Barton, 56, at a polling place in Conshohocken.

Clinton spent the final day of the increasingly sharp nominating fight touting her strength. She released an ad featuring images of al Qaeda leader Osama bin Laden and warned in an interview with ABC that, as president, she could "totally obliterate" Iran if it attacked Israel.

Clinton's last minute ad warned voters that they need to "be ready for anything" during a time of war and worsening economic prospects. "Who do you think has what it takes?" the ad's announcer asked.

Obama's camp released an ad in response. "Who in times of challenge will unite us -- not use fear and calculation to divide us?" it asked.

Obama, who would be the first black president, was on the defensive at times because of inflammatory comments of his former pastor and his own comments about the bitterness of residents in economically struggling small towns.

Clinton, who would be the first woman president, had to apologize for fabricating a story about facing sniper fire during a 1996 visit to Bosnia when she was first lady.

Clinton's husband, former President Bill Clinton, told a Philadelphia radio station on Monday the Obama campaign had "played the race card" earlier in the contest but on Tuesday sought to play down the comment.

"That's not what I said," Bill Clinton told an NBC reporter. "You always follow me around and play these little games and I'm not going to play your games today."

(Additional reporting by Jeff Mason, Caren Bohan, David Morgan and Paul Eckert; Editing by Doina Chiacu)

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(To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at http:/blogs.reuters.com/trail08/)