President Bush intends to veto a bill today that would have eased restraints on federally funded embryonic stem cell research.
Mr Bush is also expected to issue 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 could help treat illness.
White House spokesman Tony Fratto said yesterday that Bush would outline an initiative that could make federal funding available for research on additional "pluripotent" stem cells - ones that can give rise to any kind of cell in the body except those required to develop a fetus.
The president has accused majority Democrats of recycling an old measure that he already vetoed and argued that the bill would mean American taxpayers would - for the first time - be compelled to support the deliberate destruction of human embryos.
"The president supports and encourages stem cell research - including using embryonic lines - as long as it does not involve creating, harming or destroying embryos," Fratto said. "That is an ethical line that should not be crossed."
Democrats made the legislation a top priority when they took control of the House and Senate in January, but they don't have enough votes to override Bush's decision.
Senate Majority Leader Harry Reid yesterday appealed to Bush not to veto the bill. He said the measure acknowledges the ethical issues at stake and offers even stronger research guidelines than exist under the president's current policy.