The letter, which organizers believe is the biggest collection of Nobel signatures ever sent to a president, marks the latest effort to influence the Bush administration as it decides whether to fund experiments on embryonic stem cells. The cells, obtained from spare human embryos slated for destruction at fertility clinics, are widely believed to hold the potential to cure many ailments, including juvenile diabetes and Parkinson's disease.

The decision about whether to fund the work is forcing the new administration to weigh its political allegiances in an escalating battle pitting antiabortion activists against patient advocates and biomedical researchers.

Opponents of the work say the cells are ethically tainted because human embryos must be destroyed to retrieve them.

But in their letter to Bush, the Nobel laureates say that given the cells' great therapeutic promise, it would be immoral not to study them.

"While we recognize the legitimate ethical issues raised by this research, it is important to understand that the cells being used in this research were destined to be discarded in any case," the letter said. "Under these circumstances, it would be tragic to waste this opportunity to pursue the work that could potentially alleviate human suffering."

The letter is to be faxed to the White House this morning — three weeks before a National Institutes of Health deadline by which scientists must apply for the agency's planned first round of stem cell research grants.

Health and Human Services Secretary Tommy G. Thompson has said he is "reviewing" the Clinton administration's decision to fund such research, and Thompson "is cognizant of" the March 15 deadline, said HHS spokesman Campbell Gardett.

But with Thompson's review still in its early stages, and the NIH grantmaking process set to proceed, many researchers fear that Bush will not wait and instead sign an executive order blocking the funding before it begins.

The letter to Bush was signed by such notables as James Watson, who won a Nobel in 1962 for co-discovering, with Francis Crick, the structure of DNA; molecular biologist Hamilton O. Smith, who was a key player in the recent landmark genome mapping effort by Celera Genomics of Rockville; Edward Lewis, the California Institute of Technology biologist who conducted seminal work on embryo development; and Nobelists in other disciplines, including physicists Murray Gell-Mann and Steven Weinberg and economists Robert Samuelson and Milton Friedman.

The letter was composed and circulated by Michael West and Robert Lanza, two scientists at Advanced Cell Technology Inc., a biotechnology company in Worcester, Mass. Lanza said the company, which conducts stem cell research, had nothing to gain from the campaign since a Bush ban on federal funding for stem cell research would force scientists to do business with private companies such as his. Rather, he said, he was motivated by a personal wish to help patients.

"As a medical doctor and a human being, I feel obligated to do everything I can to ensure that this research reaches the clinic as soon as possible."

The letter drew sharp criticism from opponents of the research, including Douglas Johnson, legislative director for the National Right to Life Committee.

"Just as war is too important to be left only to generals, the killing of human beings in medical research is an issue too important to be left only to scientists, even Nobel laureates," Johnson said. Like other opponents, he favors research on similar cells obtained from adults — an approach that many scientists say is promising but not promising enough to justify dropping the embryo studies.

The stem cell debate that Bush inherited started when the Clinton administration determined that research on embryo cells was not prohibited by a longstanding congressional ban on embryo-destroying research. Federal researchers could not themselves destroy embryos to get stem cells, the HHS general counsel declared. But they could conduct research on cells taken from embryos that privately funded researchers had destroyed.

Opponents claim that ruling was wrong and hope that Thompson's new general counsel, yet to be named, will reverse the opinion. That would stop the grant approval process on a legal technicality without Bush having to make an executive decision.

The NIH delayed giving grant money for embryo cell research until it developed new guidelines to ensure that the research would not influence women's decisions to destroy or donate their leftover embryos. Those guidelines were finalized last year.

An NIH spokesman yesterday declined to say how many stem cell grant proposals the agency has received. Nor would he say how close the agency is to naming the members of a new advisory board that will review all such applications, or how long it might be before the first grants are approved.

"To me, it's a no-brainer," said Stanford University biologist and Nobelist Paul Berg, who signed the letter to Bush. "The cells exist and they're being destroyed and you have to decide whether you are going to just let that happen without getting any of the potential benefits."

Richard Doerflinger, of the National Conference of Catholic Bishops, disagreed. "Nobody ever said these Nobel prizes are for ethics," Doerflinger said.