PRESIDENT BUSH vowed yesterday to halt surprise new moves in Congress to lift the White House curbs on stem-cell research.

The Republican-controlled House of Representatives is poised to pass legislation that would significantly liberalise the scope of government funded scientific research into stem cells.

The prospect has alarmed Mr Bush’s aides because it would force him to confront an awkward issue that will put him at odds either with the Religious Right or Republican icons such as Nancy Reagan.

Mr Bush tried to head off the dilemma yesterday, giving warning that he would wield his first veto to block the Bill. But White House officials said that Mr Bush might support an alternative Bill allowing limited research on stem cells extracted from umbilical cord blood rather than embryos.

“We do believe that there is a lot of promise in some of the research in cord blood,” Trent Duffy, a White House spokesman, said. “The President strongly supports that kind of research. We need to look at the specifics of the kind of Bill that is being discussed on cord blood, but we think that that has some real promise.”

The issue has rocketed up the agenda as the two congressional representatives behind the Bill — Mike Castle, a Republican, and Diana DeGette, a Democrat — appear to have enough bipartisan votes to pass the measure.

The Bill would depart from the script for the second Bush term that the last presidential election appeared to deliver, a strengthened Republican majority on Capitol Hill that would do the legislative work of the Religious Right. Tom DeLay, the powerful Republican leader of the House, has set himself against the Bill but he is battling a range of ethics scandals and may not have the muscle to block it.

The Bill would expand dramatically the number of stem-cell lines available to federally funded research. Tens of thousands of embryos created through in-vitro fertilisation would become accessible to scientists.

Under Mr Bush’s 2001 compromise, only studies on existing stem-cell lines could be advanced with government money. The White House put the figure at 60, but scientists said that it was as few as 22.

The limits of the compromise have sparked complaints from universities, which are seeing their scientific talent leave. The US is in danger of falling behind countries such as Britain, Singapore and South Korea.

The pro-research lobby is headed by Mrs Reagan, whose husband died from Alzheimer’s, one of the incurable diseases and conditions that scientists say stem cells could cure.

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