Barack Obama has almost tied with Hillary Clinton in the crucial superdelegate count that she once dominated, with the slew of new support offering one of the clearest signs yet that her Democratic White House bid is nearly over.

After a gruelling duel marked by bouts of acrimony and bitterness, the Democratic race for the presidential nomination entered its final weeks, if not days, with electoral mathematics the deciding factor.

Mrs Clinton, unlikely to be able to erase Mr Obama's 1,859.5 to 1,698 lead in delegates, needs massive support from those superdelegates - party leaders free to vote as they chose - who have yet to declare their preference.

With Mr Obama also unable to reach the 2,025 delegates needed to win the nomination based solely on elected delegates, that same group offered the key to his securing the party's stamp.

The support of nine superdelegates was the latest in a steady trickle since he crushed Mrs Clinton in North Carolina and narrowly lost Indiana on Tuesday. Mrs Clinton gained two superdelegates.

Mr Obama's quiet, and increasing, confidence that the nomination is his was evident in his campaigning in Oregon, where he focused his criticism on Republican John McCain and largely ignored his Democratic rival.

The 46-year-old Illinois senator, his sights set on making history as the US's first black president, said the presumptive Republican nominee would continue failed Bush administration priorities. He pointedly criticised Mr McCain's economic, health and Iraq policies, but steered clear of criticising Mrs Clinton, continuing a strategy of avoiding antagonising her or her supporters.

Mrs Clinton, campaigning nearby in the Portland, Oregon, area, focused instead on the only real chance she had left to extend the life of her once-powerful candidacy: somehow derailing Mr Obama.

For that, she turned to the issues. At a meeting at Doernbecher Children's Hospital, she criticised Mr Obama's healthcare plan for promising universal coverage to children but not adults.

Mrs Clinton has repeatedly vowed to remain in the race until the last of the six remaining state contests is waged next month. But more than her campaign's financial woes, it was the steady stream of delegates for Mr Obama that hinted this race was nearing its end.