At first glance, the nation's emotional debate over stem cell research seems a mere rerun of the unending dispute over abortion. Both involve the same questions about protecting the development of human life, after all.

But there are important moral and religious distinctions between the two issues, and some groups that oppose abortion are not offended by stem cell experiments -- even though they necessarily destroy human embryos.

Yale University ethicist Gene Outka frames the issue partly as one of urgency -- saying that abortion involves a pressing conflict between a pregnant woman and a fetus, whereas limits on stem cell research merely affect patients who in theory might reap medical benefits at some future time.

He also notes that extraction of stem cells can be considered less morally difficult because it destroys embryos at the very earliest stage, while abortion terminates fetuses that are more developed. But some find destruction of even tiny embryos troublesome because, as Outka puts it, "the requisite genetic information renders them unique, and all of us begin at this stage."

In the religious world, thinking is varied and sometimes surprising.

The Church of Jesus Christ of Latter-day Saints, for example, is neutral on stem cells though it opposes abortion as unjustified killing except possibly in cases of incest, rape or serious peril to the mother.

The Union of Orthodox Jewish Congregations favors research if it involves frozen embryos that are left over from test-tube baby treatments. And in Islam, many jurists accept work with embryos to seek medical therapies, says Ebrahim Moosa of Duke University.

As with those Muslim thinkers, many believe that the most compelling moral argument for using embryos is that treatments using the highly adaptable stem cells could someday combat dread diseases, even though success is no certainty.

The Religious Coalition for Reproductive Choice advocates full access to abortion on behalf of mainline Protestants, Conservative and Reform Jews, Unitarians and others. The coalition believes the medical potential justifies research that employs the test-tube leftovers or aborted fetuses.

Yet even the position of that group's president, the Rev. Carlton Veazey, is nuanced. He's concerned about programs that create cloned human embryos in order to destroy them and acquire stem cells, which many in coalition churches find morally problematic. "Should we get into the business of creating and harvesting? I don't think so," he says.

Meanwhile, the California Council of Churches supports a $3 billion state program that involves stem cell harvesting through destruction of cloned embryos.

On the opposite side of the religious spectrum, the Roman Catholic Church teaches that "the life of every human being is to be respected" once a sperm and egg unite and it vehemently opposes destroying embryos, whether through abortion or for research. Eastern Orthodox and evangelical Protestant leaders generally agree.

President Bush's policy on embryonic stem cell research has been to limit federal funding to research using already existing stem cell lines because that avoids destruction of further embryos. The president has vowed to veto a bill before Congress that would provide funding for research using embryos left over from fertility treatments. (There are no legal limits on research funded by states or private sources.)

Outka, a lay Lutheran who chaired two years of Yale faculty discussions on the problem, disagrees with lay Methodist Bush. He concludes that destruction of these leftover embryos is "morally tolerable" on the "nothing is lost" argument: They're doomed to die or be discarded anyway.

But that's as far as he'll go. Outka argues in the anthology "God and the Embryo" (Georgetown University Press) that, in advocating the possible benefits of an outcome, you cannot ignore the means used to achieve it. Moral opponents of the Hiroshima bombing use the same argument.

Ethicists also worry that stem cell work is laying scientific ground for production of cloned human babies -- though research proponents emphasize the distinction between such "reproductive cloning" and research on cloned human embryos that are then destroyed.

A related argument for those who consider embryo destruction immoral is that the government should instead foster promising work with stem cells from placentas, umbilical cords and adult tissues. Last month, the President's Council on Bioethics issued a 99-page white paper on the biology and morality of four new techniques that might produce stem cells without destroying embryos.

The council's 18 members differed in their assessments but agreed that these proposals "and others like them" that could sidestep the embryo problem altogether "deserve the nation's careful and serious consideration."

Early-stage human embryos such as this cloned four-cell embryo are promising for medical research because their undifferentiated cells, or stem cells, can easily develop into any type of tissue needed in the body of a patient. President Bush, shown with families that have adopted children as embryos, says he would veto a bill to expand the stem cell research allowed with federal funding. Woo-Suk Hwang, South Korea's leading cloning expert, says the Bush administration is impeding U.S. research that could lead to major medical breakthroughs.