A new technique for growing stem cells avoids the ethical objection against destroying embryos, advocates claim, but some opponents are not convinced.

Now scientists have figured out a technique for making human embryonic stem cells without causing harm to embryos, a breakthrough that could have enormous implications for future research. Their findings are published in the journal Nature.

In July, Bush used his veto power for the first time in his entire presidency to reject legislation that would have expanded federal funding for embryonic stem cell research. However, it appears that the ethical arguments that precipitated that action may now be moot. An administration spokesperson called it a step in the right direction.

If the latest scientific claims are borne out, researchers will be able to large quantities of stem cells that could lead to new treatments for spinal cord injuries, Parkinson's disease, diabetes and other serious conditions.

Robert Lanza of Advanced Cell Technology in Massachusetts and colleagues used a technique based on pre-implantation genetic diagnosis, or PGD, to create the stem cells. PGD currently is used by fertility specialists to look for genetic defects in embryo candidates for in vitro fertilization.

To carry out PGD, a single cell is removed from the embryo when it is three days old and consists of just eight cells. The cell is tested for genetic abnormalities, and if none are found, the embryo is implanted.

In their research, Dr. Lanza's team found that a single cell taken from an embryo can be grown into many cells, some of which can then be turned into embryonic stem cells.

Although more than 2,000 babies have been born following use of the PGD technique, some scientists and ethicists are not totally convinced that it solves the stem cell dilemma. The concern has been raised that removal of the single cell might not be completely harmless and could affect the embryo's development.

The new procedure does not meet the ethical standards of the Roman Catholic church, which opposes both PGD and in vitro fertilization.

Another potential stumbling block is that the technique would not generate a large enough quantity of stem cells or that couples seeking IVF treatment would be reluctant to allow a cell to be removed from any of their embryos.

One British scientist lamented that the technique grew out of the need to circumvent political barriers rather than from purely scientific motives and suggested that all avenues of growing stem cells should be pursued.

The current procedure for growing stem cells requires the destruction of embryos when they consist of about 100 cells, after five days of development.