PRESIDENT BUSH will veto a Bill this week for the first time since he took office, when Congress is expected to pass legislation to increase federal funding for embryonic stem cell research.

Not since Thomas Jefferson, who occupied the White House between 1801 and 1809, has a US president gone this long without exercising his power of veto.

To the consternation of many Republicans, Mr Bush has finally decided to wield his veto on a politically charged issue that splits his own party, unifies Democrats and blocks a law supported by two thirds of Americans.

The Stem Cell Research Enhancement Act, which the Senate could pass today, would scrap the limits on federal funding that Mr Bush imposed in 2001.

It would channel taxpayers’ money for research using stem cells from human embryos that would otherwise have been discarded by fertility clinics.

Supporters of the Bill say that stem cell research could lead to cures for a range of life-threatening and disabling illnesses, including Parkinson’s disease, juvenile diabetes and Alzheimer’s disease.

American scientists complain that the 78 stem cell lines that were already in existence before Mr Bush’s 2001 ban are becoming unusable.

Opinion polls suggest that between 60 and 70 per cent of Americans support the legislation.

High-profile advocates have also highlighted the issue, including Nancy Reagan, the widow of Ronald Reagan, the former President, who died in 2004 after a long battle with Alzheimer’s.

The death of Christopher Reeve, the Superman actor and a prominent advocate, generated great interest in the issue during the 2004 presidential campaign, as did campaigning by the actor Michael J. Fox, a Parkinson’s sufferer.

But Mr Bush has been consistently adamant in his objection to embryonic stem cell research.

Although he supports adult stem cell studies, he says that government money should not be used to fund “science which destroys life in order to save life” and said this month that he would veto any Bill relaxing his 2001 ban.

Such a stance delights conservatives in a mid-term election year, when energising the Republican base is crucial for the party.

But it has also exposed deep divisions within the party and threatens to hurt anti-abortion Republicans in tight congressional races where the support of moderate voters is vital.

Bill Frist, the Republican Senate leader, who has been courting conservatives to enhance his presidential ambitions for 2008, reversed his opposition last year and supports the legislation, a rare show of defiance to the White House.

The Bill was passed in the House of Representatives with the help of 50 Republicans, including many who usually oppose anything that might legitimise abortion.

Democrats believe that the issue will be a vote-winner in November. Claire McCaskill, a Democrat who is challenging Senator Jim Talent, of Missouri, a conservative who opposes the Bill, highlighted the party’s support for the Bill in the Democrats’ national radio address on Saturday.

She said: “It is hard to understand that the President’s first veto in six years would amount to saying no to doctors . . . patients and families.”

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