WASHINGTON -- Twenty top Democratic donors who are supporting Hillary Rodham Clinton criticized House Speaker Nancy Pelosi in a letter asking her to retract her comments on superdelegates and stay out of the Democratic fight over their role in the presidential race.

In their letter, Clinton's supporters said superdelegates "must look to not one criterion but to the full panoply of factors that will help them assess who will be the party's strongest nominee in the general election."

The letter also noted the donors "have been strong supporters" of the House Democrats' fundraising arm. "We therefore urge you to clarify your position on superdelegates and reflect in your comments a more open view to the optional independent actions of each of the delegates at the national convention in August."

Pelosi, who has not endorsed either candidate as chair of the Democratic National Convention, said during a March 16 appearance on ABC's "This Week" that it would be harmful to the party if superdelegates don't support the pledged delegate winner.

"This is an untenable position that runs counter to the party's intent in establishing superdelegates in 1984," the letter from the wealthy Clinton backers said.

No matter what the outcome of the 10 remaining contests, it will be nearly impossible for Clinton to overcome rival Barack Obama's lead in pledged delegates, because they are awarded proportionally based on the outcome.

So it will be up to the nearly 800 superdelegates -- party activists and elected officials who aren't bound by any vote -- to put one of the two candidates over the mark of 2,024 delegates needed to win the nomination. Obama has 1,406 pledged delegates to Clinton's 1,249, according to The Associated Press count.

Obama spokesman Bill Burton said, "This letter is inappropriate and we hope the Clinton campaign will reject the insinuation contained in it."

"Regardless of the outcome of the nomination fight, Senator Obama will continue to urge his supporters to assist Speaker Pelosi in her efforts to maintain and build a working majority in the House of Representatives," Burton said.

Clinton spokesman Phil Singer said Clinton had made the case superdelegates should exercise independent judgment about who would be the best for the party and the country.

"Few have done more to build the Democratic Party than Bill and Hillary Clinton. The last thing they need is a lecture from the Obama campaign," he said.

The letter was first reported by the political blog Talking Points Memo.

The Associated Press and Reuters contributed to this report.