The Senate is debating whether to go as far as the House of Representatives has in passing legislation banning all human cloning. Proponents of an alternative measure argue for a less sweeping ban that would allow embryo cloning as a source for potentially therapeutic stem cells.

No one in Congress argues in favor of cloning humans.

Senate Judiciary Committee Chairman Dianne Feinstein says the notion of making exact genetic duplicates of a person from one of his cells is morally unacceptable.

"Cloning is one of those words and concepts that inspire dread in people, visions of an apocalyptic world marching in lock step," she said. "There is broad agreement across our society that we should ban human cloning."

Instead, the debate is over whether to prohibit cloning human embryos. They are a rich source of stem cells, immature cells that can turn into any tissue in a developing fetus. Scientists wish to mine these cells for their potential to make diseased tissue healthy again.

But the House of Representatives, controlled by President's Bush's Republican Party, passed a measure in July banning such therapeutic cloning as well as cloning to reproduce a person.

The bill's sponsor, Representative Dave Weldon of Florida, argued that destroying an embryo just days old for research purposes is taking a human life. He added that permitting embryo cloning could lead to secret reproductive cloning. "Because the implantation of the clone in a woman would occur within the privacy of the doctor-patient relationship, and because research labs throughout the United States would be producing large quantities of these embryos, it would only be a matter of time before a rogue physician in defiance of the law would implant one of these embryos in a woman," he said.

On the other side of the House debate last year was fellow Republican Party member James Greenwood of Pennsylvania, who sponsored rival legislation to permit embryo cloning for therapeutic applications.

"I wish to outlaw reproductive human cloning while permitting further and carefully circumscribed research," he said. "Unfortunately, the House chose to yield to fear mongering and voted for the Weldon bill."

Now the Senate, controlled by the opposition Democratic Party, faces the same choice. It is debating two competing measures, like those last year in the House. But unlike the House, it has a January recommendation in favor of embryo cloning to produce stem cells from a National Academy of Sciences expert panel.

The recommendation is intended to reflect the consensus of the U.S. scientific community.

"Scientists place a high value on the freedom of inquiry," said panel chair, physician Irving Weissman of Stanford University. "Recommending restriction of research is a serious matter, and the reasons for such a restriction must be compelling. There are no scientific or medical reasons to ban nuclear transplantation to produce stem cells, and such a ban would certainly close avenues of promising scientific and medical research."

But the National Academy of Sciences panel did not address the ethics of embryo cloning, which is where much of the focus of the political debate is.

President Bush mentions this often in his drive to convince Congress to adopt the more restrictive approach to cloning, as he did recently at the Medical College of Wisconsin.

"Even the most noble ends do not justify every means," the president said. "Life itself is always to be valued and protected. In biomedical research, we are dealing with the very makings of life, and the law must be firm and clear in restraining the reckless and protecting the voiceless."

The Senate is expected to vote on the competing cloning measures in March, and the tally could be close. The Democrats have a razor-thin majority, but the House Republican experience and the defection of a Senate Democrat to embryo cloning opponents show that the debate is not strictly along party lines.

Should the Senate approve the less restrictive bill, it could face a showdown with the House over how to reconcile the two versions into one that goes for President Bush's signature into law.