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 believe embryo destruction is 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."