Washington ? For all their delight in soaring voter registration and strong poll numbers, some Democrats fear the contest between Sens. Barack Obama and Hillary Rodham Clinton might have a nightmarish end, which could wreck a promising election year.

The chief worry is that Clinton may carry her recent winning streak into Pennsylvania, Indiana, North Carolina and other states, leaving her with unquestioned momentum but fewer pledged delegates than Obama.

Party leaders then would face a wrenching choice: Steer the nomination to a fading Obama, even as signs suggested Clinton could be the stronger candidate in November; or go with the surging Clinton and risk infuriating Obama’s supporters, especially blacks, the Democratic Party’s most loyal base.

Some anxious Democrats want party elders to step in now to generate more “superdelegate” support for Obama, effectively choking off Clinton’s hopes before she can bolster them further. But many say that is unlikely, and they pray the final 10 contests will make the ultimate choice fairly obvious, not excruciating.

Barring a complete meltdown by Obama, Clinton has almost no chance of surpassing his number of pledged delegates, even if she scores upset wins in states such as Oregon, which votes May 20.

But such victories would encourage her to keep criticizing Obama – her only hope for the nomination – and thus heighten doubts about Obama’s ability to defeat Republican Sen. John McCain in the fall.

That scenario troubles many Democrats, especially those who feel Obama’s nomination is all but inevitable.

“This is going to give Republicans a chance to try to destroy everything we’ve been trying to work for for eight years,” said Ken Foxworth, a Democratic National Committee member from Minnesota and superdelegate who backs Obama.

Superdelegates are party officials, including members of Congress, who can back any candidate they wish. With neither Obama nor Clinton able to secure the nomination with the pledged delegates they win in primaries and caucuses, the superdelegates ultimately will decide the outcome.

Many undeclared superdelegates express confidence that all will be well. Democratic voters will unite in the fall, they say, and the injuries that Obama and Clinton inflict on each other this spring will heal.

Privately, however, some party insiders worry that these superdelegates may be blithely marching toward a treacherous crossroad, where they will have to choose between a deeply wounded Obama and a soaring Clinton whose success was built on tearing down the party’s front-runner in terms of delegates.

A senior Democratic Senate aide, who would speak only on background because most members of Congress bar their staff members from being quoted by name, called it a nightmare that’s getting worse.