With the active encouragement of the Bush administration, U.S. scientists in the past year have developed several methods for creating embryonic stem cells without having to destroy human embryos.

But some who now wish to test their alternatively derived cells have found themselves stymied by an unexpected barrier: President Bush's stem cell policy.

The 2001 policy says that federal funds may not be used to study embryonic stem cells created after Aug. 9 of that year. It is based on the assumption that the only way to make the cells is by destroying human embryos -- a truism in 2001 but not any longer.

As a result, the National Institutes of Health recently refused to consider a grant application for what would have been the first federal study to compare several of the new, less politically contentious stem cell lines.

"This is not the way to make good health policy," said Robert Lanza, the frustrated vice president for research and scientific development at Advanced Cell Technology (ACT) in Worcester, Mass. Lanza submitted the study proposal with stem cell experts from several major research labs.

Upcoming changes in the NIH's stem cell funding rules may eventually help resolve that problem. But agency officials and others say the policy tangle is more complicated than that. Although Lanza's technique and other new approaches do not destroy embryos, they may run afoul of a long-standing congressional ban on studies that "harm" human embryos.

That vague language raises the perplexing question of how one would know whether an embryo had been harmed.

At the center of the debate is a new technique, pioneered by ACT, that obtains stem cells from human embryos while leaving the embryos functionally intact. A single cell, called a blastomere, is removed from an eight-cell human embryo, then coaxed to multiply into a colony of stem cells in a dish.

Fertility doctors have been performing these blastomere biopsies for years to identify embryos that harbor genetic defects. Since a single cell is representative of the entire embryo, doctors transfer to a mother-to-be's womb only those embryos whose plucked cells pass genetic muster. The loss of a single cell -- or even two -- at that stage is not known to cause developmental problems in children born by this procedure, doctors say.

In unpublished research, ACT has made several colonies of stem cells this way, Lanza said. The seven-cell embryos developed normally and were frozen after the procedure a couple of days later, as embryos typically are until used by infertile couples.

The question is whether stem cells made this way are as versatile as those harvested from destroyed embryos. And what about stem cells created by other means, such as those of Anthony Atala, the Wake Forest University scientist who in January announced he had isolated embryonic stem cell equivalents from amniotic fluid?

To find out, Lanza joined with Atala and a team of others to compare stem cells made by various means. The group submitted a proposal to the NIH in February, then waited. And waited.