http://www.nytimes.com/2005/07/29/politics/29stem.html?pagewanted=print

WASHINGTON, July 28 - In a break with President Bush, the Senate Republican leader, Bill Frist, has decided to support a bill to expand federal financing for embryonic stem cell research, a move that could push it closer to passage and force a confrontation with the White House, which is threatening to veto the measure.

Mr. Frist, a heart-lung transplant surgeon who said last month that he did not back expanding financing "at this juncture," is expected to announce his decision Friday morning in a lengthy Senate speech. In it, he says that while he has reservations about altering Mr. Bush's four-year-old policy, which placed strict limits on taxpayer financing for the work, he supports the bill nonetheless.

"While human embryonic stem cell research is still at a very early stage, the limitations put in place in 2001 will, over time, slow our ability to bring potential new treatments for certain diseases," Mr. Frist says, according to a text of the speech provided by his office Thursday evening. "Therefore, I believe the president's policy should be modified."

Mr. Frist's move will undoubtedly change the political landscape in the debate over embryonic stem cell research, one of the thorniest moral issues to come before Congress.

The stem cell bill has passed the House but is stalled in the Senate, where competing measures are also under consideration. Because Mr. Frist's colleagues look to him for advice on medical matters, his support for the bill could break the Senate logjam. It could also give undecided Republicans political license to back the legislation, which is already close to having the votes it needs to pass the Senate.

But the move could also hinder Mr. Frist's own political prospects. He is widely considered a potential candidate for the presidency in 2008, and supporting an expansion of the policy will put him at odds not only with the White House, but also with Christian conservatives, whose support he will need in the race for the Republican nomination.

"I am pro-life," Mr. Frist says in the speech, arguing that he can reconcile his support for the science with his own Christian faith.

"I believe human life begins at conception."

But at the same time, he says, "I also believe that embryonic stem cell research should be encouraged and supported."

Backers of the research were elated.

"This is critically important," said Larry Soler, a lobbyist for the Juvenile Diabetes Research Foundation. "The Senate majority leader, who is also a physician, is confirming the real potential of embryonic stem cell research and the need to expand the policy."

Mr. Frist has been under pressure from all sides on the embryonic stem cell debate. Some of his fellow Senate Republicans, including Orrin G. Hatch of Utah and Arlen Specter of Pennsylvania, who is the lead Senate sponsor of the House bill, have been pressing him to bring up the measure for consideration. But with President Bush vowing to veto the measure - it would be the first veto of Mr. Bush's presidency - other Republicans have been pushing alternatives that could peel support away from the House bill.

Last week, the chief sponsor of the House measure, Representative Michael N. Castle, Republican of Delaware, accused the White House and Mr. Frist of "doing everything in their power to deflect votes away from" the bill, "or keep it coming up for a vote at all."

Despite Mr. Frist's speech, a vote on the bill is not likely to occur before September because the Congress is scheduled to adjourn this weekend for the August recess.

With proponents of the various alternatives unable to agree on when and how to bring them up for consideration, Mr. Frist says he will continue to work to bring up all the bills, so that senators can have a "serious and thoughtful debate."

Human embryonic stem cells are considered by scientists to be the building blocks of a new field of regenerative medicine. The cells, extracted from human embryos, have the potential to grow into any type of tissue in the body, and advocates for patients believe they hold the potential for treatments and cures for a range of diseases, from juvenile diabetes to Alzheimer's disease.

But the cells cannot be obtained without destroying human embryos, which opponents of the research say is tantamount to murder. "An embryo is nascent human life," Mr. Frist says in his speech. "It's genetically distinct. And it's biologically human. It's living. This position is consistent with my faith. But, to me, it isn't just a matter of faith. It's a fact of science."

On Aug. 9, 2001, in the first prime-time speech of his presidency, Mr. Bush struck a compromise: he said the government would pay only for research on stem cell colonies, or lines, created by that date, so that the work would involve only those embryos "where the life or death decision has already been made."

The House-passed bill would expand that policy by allowing research on stem cell lines extracted from frozen embryos, left over from fertility treatments, that would otherwise be discarded. Mr. Castle has said he believes the bill meets the president's guidelines because the couples creating the embryos have made the decision to destroy them.

In his speech, Mr. Frist seems to adopt that line of reasoning, harking back to a set of principles he articulated in July 2001, before the president made his announcement, in which he proposed restricting the number of stem cell lines without a specific cutoff date. At the time, he said the government should pay for research only on those embryos "that would otherwise be discarded."

When Mr. Bush made his announcement, it was widely believed that as many as 78 stem cell lines would be eligible for federal money. "That has proven not to be the case," Mr. Frist wrote. "Today, only 22 lines are eligible. Moreover, those lines unexpectedly after several generations are starting to become less stable." Even so, Mr. Frist says the Castle bill has serious shortcomings, in his view. He says it "lacks a strong ethical and scientific oversight mechanism," does not prohibit financial incentives between fertility clinics and patients, and does not specify whether the patients or the clinic staff have a say over whether embryos are discarded. He also says he does not like the idea that the new policy would be in place indefinitely.

"This concerns me," Mr. Frist says in the speech, "because the science of stem cell research is evolving in so many different ways."

Mr. Frist also says he supports some of the alternative measures, including bills that would promote research on so-called adult stem cells and research into unproven methods of extracting stem cells without destroying human embryos.

"Cure today may be just a theory, a hope, a dream," he says, in the conclusion of the text. "But the promise is powerful enough that I believe this research deserves our increased energy and focus. Embryonic stem cell research must be supported. It's time for a modified policy - the right policy for this moment in time."