Democratic presidential hopeful Sen. Barack Obama, D-Ill., takes a sip of a Yuengling beer after shaking hands Friday in Sharky's Cafe in Latrobe, Pa.

Pittsburgh ? Barack Obama got a surprise boost in the last big state of the long Democratic campaign Friday with an endorsement from Pennsylvania Sen. Bob Casey Jr., while another Obama supporter sought to nudge Hillary Rodham Clinton out of the race.

Clinton leads by double-digits in Pennsylvania polls, and Obama hopes Casey’s endorsement will earn him a second look from the state’s white, working class and Catholic voters – groups that have leaned toward Clinton in other Democratic contests this year.

Clinton, on the other hand, is hoping a victory in Pennsylvania will help persuade party “superdelegates” to support her and allow her to catch Obama in the race for National Convention delegates.

Sen. Patrick Leahy, a Vermont senator who endorsed Obama in January, said she was never going to win enough delegates, and he suggested she should throw in the towel in “the interests of a Democratic victory in November.” A number of Democrats have expressed concern that Republican John McCain is getting a head start while Obama and Clinton fight on.

Undeterred, Clinton said the competition would only strengthen the party in the long run.

“This spirited, exciting contest is actually a real plus for us,” she said while campaigning in Indiana, which has its primary two weeks after Pennsylvania’s April 22 vote.

McCain launched his first television ad of the general election campaign Friday, portraying himself as a courageous leader with the knowledge and experience to keep the country safe as a wartime commander in chief. “The American president Americans have been waiting for,” the ad says, juxtaposing footage of the Arizona senator with clips of him as a prisoner of war in Vietnam three decades ago.

Casey, the son of a popular late governor, had said earlier this month he would not endorse before the Pennsylvania primary out of concern for party unity. But he joined Obama at a boisterous rally kicking off a six-day bus trip through the state, where current Gov. Ed Rendell has been campaigning hard for Clinton.