Pennsylvania Democrats cast votes

WASHINGTON (Reuters) - Democrats in Pennsylvania make theirchoice on Tuesday in the presidential nominating race betweenHillary Clinton and Barack Obama, with Clinton aiming for a bigwin to keep her flickering White House hopes alive.

The New York senator is favored in Pennsylvania, but needsa convincing victory to gain ground on Obama in the Democraticrace and convince party leaders she is the best candidate toface Republican John McCain in November's presidentialelection.

Voting in Pennsylvania, the first state to cast ballots insix weeks, closes at 8 p.m. EDT (1 a.m. British time) and thefirst results will be available soon afterward.

Clinton's one-time 20-point lead has slipped to singledigits in many polls amid an onslaught of advertisements byObama, who has heavily outspent her in the state. But bothcamps tried to play down expectations ahead of the vote.

"I'm not predicting a win. I'm predicting it's going to beclose and that we are going to do a lot better than peopleexpect," Obama told a Pittsburgh radio station on Monday.

The two candidates spent the final day of an increasinglysharp fight scouring the state for last-minute support. Clintonreleased an ad featuring images of al Qaeda leader Osama binLaden and touting her strength.

"You need to be ready for anything -- especially now, withtwo wars, oil prices skyrocketing and an economy in crisis,"the ad's narrator says. "Who do you think has what it takes?"

Obama's camp accused her of using "the politics of fear"and he released his own ad in response. "Who in times ofchallenge will unite us -- not use fear and calculation todivide us?" the ad asked.

The Pennsylvania vote opens the final phase of Clinton andObama's hard-fought duel for the nomination. Nine more contestsare scheduled before the campaign concludes on June 3.

CLINTON HOPES FOR BIG WIN

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

Clinton hopes a big win in Pennsylvania ignites a strongrun through the last nine contests, convincing superdelegatesshe is the candidate who can capture the big states that willbe crucial in November.

A narrow Clinton win would probably keep her in the race,but not stem another round of calls among Democrats for her tostep aside and let Obama focus on the race with McCain.

"Someone's going to be the nominee and I think that someoneis going to be Barack Obama. But it will take some time," Obamastrategist David Axelrod told reporters.

In contrast, an Obama win would almost certainly increasepressure on Clinton to drop out of the race and ignite a moveby superdelegates toward the Illinois senator.

The two candidates spent the weeks before the vote battlingcampaign controversies and courting Pennsylvania's big bloc ofblue-collar voters. Obama went bowling and hoisted beers withvoters, while Clinton went door-to-door in working classneighbourhoods.

Obama was on the defensive at times over the inflammatorycomments of his former pastor and his own comments about thebitterness of residents in economically struggling small towns.

Clinton had to apologize for fabricating a story aboutfacing sniper fire during a 1996 visit to Bosnia when she wasfirst lady.

The Pennsylvania contest is the latest in a series ofdo-or-die votes for Clinton, who rallied from the brink ofelimination with a win in New Hampshire on January 8 andpopular vote victories in Ohio and Texas on March 4.

(Editing by Todd Eastham)

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