To blunt criticism, Bush issued an executive order directing the Health and Human Services Department to promote research into cells that — like human embryonic stem cells — also hold the potential of regenerating into different types of cells that might be used to battle disease.

His spokesman, Tony Snow, said the executive order encouraged scientists to work with the government to add research on new stem-cell lines — those that don't involve the creation, harming or destruction of human embryos — to the list of projects eligible for federal funding.

In 2001, Bush banned federal funding for research using embryonic stem cells but exempted projects using already established embryonic stem-cell lines. New lines, however, cannot be created using federal funding, and it will not pay for projects using them, although states and private organizations can pay for it. The bill would have lifted that restriction.

Bromberg said the stem-cells lines that qualify for federal funds are "old and obsolete" now. And new methods developed since then have allowed researchers to produce embryonic stem-cell lines with a "much purer yield of stem cells."

Supporters of the embryonic stem-cell research have a long list of conditions they believe it might cure, but even the most optimistic say it will take time for the research and anything it yields to actually affect people who suffer from a condition.

"We have made progress in the past couple of years, but it's going to continue to be slow progress," Dr. Linda Kelley, director of the cell-therapy program at the U., told the Deseret Morning News when the issue surfaced in January.

What is clear, said Beckerle, is that embryonic stem cells can become many different types of cells — with the potential to be useful to repair different types of tissues.

Senate Majority Leader Harry Reid is expected to schedule an override vote, but the date has not been set. Democrats, however, currently do not have enough votes to override Bush's veto.

Meanwhile, public opinion polls show strong support for the research, and it could return as an issue in the 2008 elections.

Opponents of the latest stem-cell measure insisted that the use of embryonic stem cells was the wrong approach on moral grounds — and possibly not even the most promising one scientifically. These opponents, who applaud Bush's veto, cite breakthroughs involving medical research conducted with adult stem cells, umbilical cord blood and amniotic fluid, none of which involve the destruction of a human embryo.

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E-mail: lois@desnews.com