The Senate is on the threshold of a momentous decision: whether to expand research on human embryonic stem cells. In casting their votes, senators must decide whether to support the judgment of a large, bipartisan House majority (and an overwhelming majority of scientists and the public) or to further delay vital medical research.

Given the general agreement that such research has the potential to relieve the misery and suffering of millions, we find it troubling that opponents of this legislation (H.R. 810 or S. 471) are trying to divert the debate about the merits of expanding this research by promoting dubious approaches to obtaining stem cells that even their supporters concede are scientifically and ethically problematic. What is so bizarre about this effort is that there is no need for the administration and its congressional followers to seek authorization to pursue these proposed "new" approaches for obtaining stem cells. Research on these proposed alternatives is already legal and can be funded by existing mechanisms.

We want to be very clear: The most successful demonstrated method for creating the most versatile type of stem cells capable of becoming many types of mature human cells is to derive them from human embryos -- at present, excess embryos created at in vitro fertilization clinics and freely donated for research by couples who choose not to have them destroyed as medical waste.

While some of the proposed alternatives being suggested may have some promise, they are unproven. Some, in fact, are ethically questionable when performed with human tissues. One idea is to derive stem cells from embryos that have stopped developing and are thought to be "biologically dead." Beyond the fact that scientists haven't developed a reliable method for determining an embryo's "death," there is no scientific evidence that stem cells derived from these embryos would have the required properties or be safe for human therapies.

Another set of proposals focuses on attempts to reprogram adult cells to revert to an early, undifferentiated, stem cell-like stage of development. This is an important, though highly speculative and ambitious, goal. Indeed, it is a goal that developmental scientists are already seriously investigating today, but with many uncertainties about whether and how it can be made practical. Still another proposal is to separate a single cell from a live embryo while attempting to preserve the embryo's potential to initiate a pregnancy and normal birth. This proposal is not only speculative but poses ethical concerns as to possible damage that might be inflicted on the embryo.

In a July 12 op-ed in The Post, Leon R. Kass, chairman of the President's Council on Bioethics, wrote: "It may be that some opponents of embryo research are using these worthy proposals for . . . a political purpose." We agree: It is likely that some opponents are pursuing a political purpose in their public embrace of these proposals. We also agree that federal funding for these and many other proposed options, including adult stem cell research, should continue to be provided.

But it needs to be understood that most of the proposed alternatives are not restricted by a presidential executive order, although they may run afoul of other federal restrictions on research with human embryos. Interested scientists need only write a grant proposal and pass the scientific peer review process for technical merit to secure funding for the research. It is the president's executive order of Aug. 9, 2001, that is impeding research progress in bringing potential stem cell therapies to the clinic. That is why legislation to lift the federal limits on research with human embryonic stem cells should be passed.

We urge Congress to deal with this matter on its scientific merits without raising a laundry list of other speculative scientific approaches that serve only to confuse the issue. The treatment of otherwise intractable diseases can become a reality if we expand the number and quality of the stem cells that American scientists have to work with.

Paul Berg is emeritus professor in cancer research at Stanford University. George Q. Daley is an associate professor at Harvard Medical School and associate director of the stem cell program at Children's Hospital in Boston. Lawrence S.B. Goldstein is a professor of cellular and molecular medicine at the University of California at San Diego School of Medicine and an investigator at the Howard Hughes Medical Institute.