FAIRLESS HILLS, Pennsylvania (AP):

Facing a revived Hillary Rodham Clinton, Democrat Barack Obama has dropped a tenet of his early strategy that seemed vital to his January successes: the conviction that he can win almost anywhere if he has enough time to engage voters.

With the important Pennsylvania contest six weeks away - a near eternity in presidential primaries - Obama is playing down his chances in the northeastern state, even though a victory would effectively finish Clinton. His aides are emphasising instead the need to campaign in North Carolina, Indiana and other presumably friendlier states that will vote even later.

Clinton, meanwhile, is banking heavily on Pennsylvania. A solid win here could sustain her claim to late-season momentum and the ability to win big industrial states.

The New York senator travelled to Pennsylvania immediately after the March 4 primaries when her Ohio and Texas wins kept her campaign alive. Obama did not go until Tuesday, a full week later. He held one public event, north of Philadelphia, before returning to Chicago for a day.

Obama's revised strategy is, essentially, a mathematical calculation. If Clinton wins a few more delegates than he does in Pennsylvania, Obama figures, he can offset them in the nine states and territories scheduled to vote later.

His current lead of roughly 100 delegates would stay about the same, the thinking goes. That would position him to tell the all-important superdelegates this summer there is no justification for them to tip the nomination to Clinton.

Superdelegates are party and elected officials who can side with any candidate. They will decide the nomination because neither Obama nor Clinton can secure enough pledged delegates through voting rules that allocate state delegates on a proportionate, not winner-take-all, basis.

The strategy may be politically sound. But it lacks the swagger and self-confidence that Obama carried out of Iowa into South Carolina and beyond.