Washington ? Will he or won’t he? Supporters of a bill to allow federal financing of embryonic stem cell research are hoping something will happen to change President Bush’s mind about vetoing the measure awaiting Senate approval.

It would be Bush’s first veto of any legislation but – so far – the president appears to be standing firm in his determination to block the stem cell bill.

Neither the House nor Senate has demonstrated enough support to override a veto, though the House probably will try, just to give Bush a definitive victory in the showdown.

Supporters of the research hold out faint hope that Bush, presented with new data and pressured by election-year politics, might reverse course and sign the bill.

“This would be his first veto in six years, on something that the vast majority of the public supports,” said Sen. Tom Harkin, D-Iowa. “What would come down on him would be all the scientists, all the Nobel laureates and everyone else who supports it.”

Polls show that 70 percent of the public supports the bill, which would expand federal aid for embryonic stem cell research. The process is believed by many scientists to hold the most promise for curing diseases such as juvenile diabetes, Alzheimer’s and Parkinson’s that strike millions of people.

The bill comes before the full Senate at the same time that Republicans, with their congressional majority at stake, are trying to energize their conservative base of voters during the fall elections.

Set for House action are bills to protect the Pledge of Allegiance from court challenges and a constitutional amendment to ban gay marriage, which failed in the Senate. Bills to encourage stem cell research from sources other than embryos also are expected to be voted on this week.

But it is the Senate’s stem cell bill that probably will draw the most attention – and Bush’s first veto.

In 2001, Bush halted federal funding of new embryonic stem cell studies, comparing them to abortion because the process of extracting the crucial stem cells destroys the days-old embryo.

He said at the time that such federal support for research could continue on the 78 stem cell lines then thought to exist. But in the years since, the National Institutes of Health have confirmed that a fraction of that number of lines exist and that few, if any, are viable for clinical trials.

Supporters hope that development might change Bush’s mind. But the White House, struggling for election-year credibility with its conservative base, has left no wiggle room in its public and private statements of opposition.

Several lawmakers who have spoken to Bush, adviser Karl Rove and other White House officials in the year since the House passed the bill say they consistently have rejected any talk of compromise.

Rove last week said Bush was “emphatic” about his intent to veto the bill. White House spokesman Ken Lisaius said Friday the president would follow through if the bill came to him.

That could happen this week. Vote counters on both sides of the debate in the Senate say at least 60 votes for the bill exist – perhaps as many as 64; that’s enough to pass it. But 67 votes would be required to overturn a veto if all 100 senators are present.

The House was 50 votes short of its two-thirds majority when it passed the bill last year, 238-194. House leaders were planning for a veto override attempt as soon as Bush vetoes it, probably before week’s end.