Senate Majority Leader Bill Frist (R-Tenn.) today announced that he will support a bill that loosens federal prohibitions on human embryonic stem cell research, a decision that puts him at odds with the Bush administration.

Frist, a heart transplant surgeon who opposes abortion, said on the Senate floor early this morning that "embryonic stem cells uniquely hold specific promise for some therapies and potential cures."

The issue has been extremely controversial on Capitol Hill because proponents of such research say that these cells may provide treatments for major diseases, such as diabetes, cancer and Parkinson's. But some people who oppose abortion believe that the cells should not be used because they are extracted from human embryos. These critics argue that other options, including stem cells from adults, could eventually provide the same therapeutic advantages.

Frist acknowledged that adult stem cells may someday alleviate the need for embryonic cells. But he said research needs to go forward on the embryonic cells because they have the "remarkable capacity to become any kind of tissue" and are able to replicate indefinitely.

"I'm a physician. My profession is healing . . . ," Frist said. "In all forms of stem cell research, I see today, just as in 2001, great, great promise to heal. Whether it is diabetes or Parkinson's disease, or my own field of heart disease, Lou Gehrig's disease or spinal cord injuries, stem cells offer hope for treatment that other lines of research simply cannot offer."

The bill, which passed the House in May, would allow federal funds to be used in research on stem cells derived from human embryos that are slated to be destroyed by infertility clinics because they are no longer needed by patients. The Senate has not yet scheduled debate on the bill and six alternatives are being offered by senators opposed to funding of such research.

President Bush, who established strict limits to stem cell research supported by federal dollars early in his first term, has threatened to veto the bill.

White House spokesman Scott McClellan told the Associated Press that Frist gave Bush advance notice of his announcement and "the president said, 'You've got to vote your consciences.' " McClellan said the president has not altered his views of the bill.

Because of his medical background, Frist's views of bioethical issues have been influential on Capitol Hill in the past. But he came under strong criticism earlier this year for helping guide emergency legislation through Congress that ordered federal courts to review the case of Terri Schiavo, a brain damaged Florida woman whose feeding tube was removed, and questioning whether she was in a "persistent vegetative state" after he viewed her on a videotape.

Under the rules set by Bush in August 2001, federal funds can be used to study only those stem cell colonies that had been derived at that time. But critics maintain that many of those colonies are not useable, and Frist pointed out today that even those that can be used are not the best possible options.

"When the president announced his policy four years ago, it was widely believed . . . that there would be 78 embryonic stem cell lines available for federal funding. This has proven not to be the case," Frist said. "Today only 22 lines are eligible. Moreover those lines, unexpectedly, after several generations, are starting to become less stable and less replicative than initially thought."

He said that current limitations "will over time slow our ability to bring potential new treatments for certain diseases. Therefore I believe the president's policy should be modified."

Frist said he would support the House bill only if certain changes were made. He wants more oversight established for such research programs and he said parental approval must be given for the use of any embryos.

His comments were immediately hailed by the advocates of stem cell research. Former first lady Nancy Reagan, who has supported such study as part of her advocacy for a cure for Alzheimer's disease, told AP that she endorsed Frist's move because stem cell therapy "has the potential to alleviate so much suffering."

Sen. Harry Reid (D-Nev.), the minority leader, said Frist's decision "will bring hope to millions of Americans who face these horrible diseases."

Sen. Arlen Specter (R-Penn.), who is battling cancer, called the speech the most important one on the Senate floor this year. "This is a speech that will be heard around the world, especially at the White House. . . . I know that the president will listen to what Sen. Frist had to say."

Shortly after his speech, Frist appeared at the White House with Bush for a bill signing ceremony. They shook hands and talked lightheartedly at the occasion.

Conservative groups, however, were quick to complain.

"Senator Frist cannot have it both ways. He cannot be pro-life and pro-embryonic stem cell funding," the Rev. Patrick J. Mahoney, director of the Christian Defense Coalition, told the AP. "Nor can he turn around and expect widespread endorsement from the pro-life community if he should decide to run for president in 2008."