WASHINGTON  Leading contributors to Senator Hillary Rodham Clinton intensified their effort to keep the Democratic presidential contest alive on Wednesday and urged Speaker Nancy Pelosi to stay out of the superdelegate fight, admonishing her for suggesting that the candidate ahead in pledged delegates  now Senator Barack Obama  should become the nominee.

“This dynamic primary season is not at an end,” said a letter to Ms. Pelosi, which was signed by 21 top Democratic fund-raisers. “Several states and millions of Democratic voters have not yet had a chance to cast their votes.”

The letter, which carried threatening overtones in noting that many signatories were major Democratic donors, highlighted the deepening rift inside the party among supporters for Mrs. Clinton and Mr. Obama. While Ms. Pelosi has declared her neutrality in the race, she has said that she believes that the party’s superdelegates should not overrule the will of the voters and should back the candidate with the most pledged delegates.

As former President Bill Clinton warned voters in West Virginia to “saddle up” for a heated duel between the candidates, the Clinton supporters asked Ms. Pelosi to “reflect in your comments a more open view to the optional independent actions of each of the delegates” at the convention. In a statement Wednesday evening, a spokesman for Ms. Pelosi said the speaker believed that the fight should be resolved before the convention.