The Senate’s stem-cell debate forces a moment of truth upon Majority Leader Bill Frist (R-Tenn.): Is he, at bottom, a doctor and scientist dedicated to saving lives, or just an ambitious politician out to advance his career?

At the moment, the evidence suggests the latter — that he’s working to peel votes away from legislation that would hasten stem-cell research, and in the process give himself and his party political cover. [IMGCAP(1)]

Polls consistently show that as many as two-thirds of voters support federal funding of medical research using embryos left over at in-vitro fertilization clinics and otherwise destined for destruction. Even many evangelical Christians and Roman Catholics support the research.

But the religious right wing of the Republican party and the right-to-life movement — which probably have veto power over GOP presidential nominees — strongly oppose the research on the grounds that the embryos constitute sacrosanct “human life.”

To the dismay of many who admire him, this would not be the first time Frist has allowed his ambition to trump his scientific judgment and put him in league with the ideologues.

In July 2001, after serious study and soul-searching, he bucked the right wing and endorsed federal funding of embryonic research within proper ethical guidelines.

But then in August 2001, Frist saluted when President Bush limited the funding to stem cells obtained prior to that time and supported the Bush claim that researchers would have as many as 60 batches (or “lines”) of stem cells to work with.

It turns out that only 22 lines are available and all are contaminated, making them unsuitable for use in humans.

The current Senate fight pits those who want to eliminate Bush’s restrictions — including most scientists and disease advocacy groups who are eager for robust stem-cell research — and the ideologues who are trying to retain them.

Pro-stem-cell forces, led by Sens. Arlen Specter (R-Pa.), Orrin Hatch (R-Utah) and Tom Harkin (D-Iowa), are working to win 60 votes — or possibly 67, enough to override a presidential veto — for H.R. 810, which passed the House in May by a vote of 238-194.

But Frist is working to fashion an alternative bill being drafted by Sen. Mike Enzi (R-Wyo.) that would retain the Bush limits and, for political cover, back new techniques for deriving stem cells without destroying embryos.

Those voting for the Enzi measure could claim they support stem-cell research; however, abundant scientific testimony indicates that the alternative methods, while promising in some cases, would delay potential discovery of treatment for such afflictions as Parkinson’s Disease, juvenile diabetes and spinal cord injury. (As readers may know, I’m not objective on this subject. My wife, Milly, died of Parkinson’s last year, and I am on the board of the Parkinson’s Action Network and the Michael J. Fox Foundation for Parkinson’s Research.)

At a Senate press conference last week, Fox stated what most disease advocates firmly believe: that all avenues of stem-cell research should be vigorously pursued.

If alternatives to embryonic research prove to have greater potential to produce cures, they should — and inevitably will — win out in the race for scientific backing.

But as Frist himself said in 2001, “research using the more versatile embryonic stem cells has greater potential than research limited to adult stem cells and can, under the proper conditions, be conducted ethically.”

“Adult” stem cells — obtained from umbilical cords, placentas, skin or other tissue — offer an alternative line of research, one that is being actively pushed by the Bush administration. It should be — but not to the exclusion of embryonic stem-cell research.

Some of the proposed alternatives are more speculative, and some of them involve ethical difficulties of their own. One of them, for instance, calls for removing a single cell from a live embryo, potentially altering its nature should it ever be implanted in a woman’s uterus.

Another, known as “altered nuclear transfer,” involves creating an embryo with a genetic defect that makes it impossible to develop into a human. This technique raises the question of whether stem cells so derived would be human.

Other techniques have been floated, but all are theoretical, whereas it’s clear that cell lines can be derived now from leftover embryos.

The stem-cell controversy is only the latest in which Frist has dismayed admirers of his record as a physician. Bowing to the right, he relied on old videos of brain-damaged Terry Schiavo to determine that she should be kept alive.

In Frist’s defense, it could be said that, as the Republican leader, he has an obligation to support Bush. But should he do so when it’s clear that Bush policy flies in the face of life-saving science?

Historically speaking, Frist clearly would not be the first would-be president to abandon principle in the short run, believing he could do greater good in the long run.

Lyndon Johnson is the model. He spent decades toeing the segregationist Southern line — even opposing anti-lynching laws — to gain the power that eventually allowed him to pass civil rights laws.

Ronald Reagan, though no racist, chose to launch his 1980 presidential campaign in Philadelphia, Miss., scene of the infamous 1964 murder of three civil rights workers, sending a distinct message to Southern voters.

Bill Clinton, to prove he was not soft on crime as he ran for president in 1992, refused to halt the execution of a mentally retarded Arkansan, Ricky Ray Rector.

Moreover, Frist may calculate that even if the House stem-cell bill passes the Senate, Bush will surely veto it and the House will not override the veto. If so, standing up to the right in this case would be a waste of effort and political capital.

But this begs the question: When, if ever, will he stand up? Frist has saved thousands of lives as a heart surgeon. He means to save millions more as an advocate for worldwide disease prevention and treatment.

Right now, though, he faces a choice: to do what is right and to help millions who might benefit from research he knows is desirable, or to hold it back in the name of personal advancement.