A leading Democratic supporter of embryonic stem cell research said Tuesday he believes the Senate has enough votes to overcome a promised veto by President Bush, while a top GOP advocate wasn’t so sure.

As the Senate opened debate on a bill (S 5) that would allow expanded federal funding of embryonic stem cell research, supporters tried to sway enough lawmakers so they reach the two-thirds majority needed for a veto override — 67 if all senators vote. They’re sharing the stage this week with cosponsors of a second measure (S 30) that would authorize increased funding for stem cell research without allowing the destruction of embryos.

Embryonic stem cell research is a divisive issue that doesn’t split cleanly along party lines. Opponents liken the research to abortion because embryos are destroyed, and they say it is not only unethical but also unproven. Supporters, however, see embryonic stem cell research as holding great promise for curing many diseases and conditions, including cancer and diabetes.

If the embryonic research bill becomes law, it would reverse Bush’s ban on federal research funding for stem cell lines created after Aug. 9, 2001.

The November 2006 elections delivered several new Democratic senators who back the embryonic research bill, but Tom Harkin, D-Iowa, and other supporters appear to be one vote short of an override. That wasn’t Harkin’s outlook Tuesday; he expressed optimism about finding the extra vote but did not provide a name.

“I really do believe we have the 67 votes,” he said. “I’ll be surprised if we don’t.”

Harkin’s partner across the aisle, Orrin G. Hatch, R-Utah, had a different calculation. “I think we could have as many as 66 [votes], counting Tim Johnson,” said Hatch, an opponent of abortion rights but a supporter of embryonic stem cell research.

The absence of Johnson, D-S.D., who is recovering from a brain hemorrhage he suffered late last year, would not affect the two-thirds majority required for an override.

Harkin acknowledged that he may have to be patient before knowing whether his prediction holds true.

“Let’s wait and see what happens here,” he said. “Sometimes people vote for veto overrides that don’t vote for the bill.”

Harkin, Hatch and other senators were quick to point out the recent policy defection of Bush’s director of the National Institutes of Health, Dr. Elias Zerhouni. In March, Zerhouni broke with the administration by saying a change in the president’s policy on embryonic research would be better for science and the nation.

Hatch said politicization of the issue has scared off some potential GOP supporters. “I think there are a number who wish they could vote on this,” said Hatch, who also wouldn’t provide any names.

The bill is expected to easily garner the 60 votes required under Senate rules for passage. A spokesman for Majority Leader Harry Reid, D-Nev., the sponsor of the embryonic research bill, said votes on both measures are “likely” Wednesday evening. No amendments will be allowed.

The House passed a companion bill (HR 3) in January, 253-174, but is nowhere near the two-thirds needed for an override. It is expected to clear the Senate bill, giving that chamber the first try for an override vote.

The bill’s supporters had targeted freshman Democrat Bob Casey of Pennsylvania as a possible swing vote, but late last week, Casey said he will vote against the bill and a veto override.

Without Casey, supporters may turn to John E. Sununu, R-N.H., or Ben Nelson, D-Neb., who both voted against similar legislation in 2006.

Earlier Tuesday, the White House issued two statements of administration policy, one in which Bush vowed to veto the embryonic stem cell measure and another that expressed strong support for the other bill.

That measure, cosponsored by Republicans Norm Coleman of Minnesota and Johnny Isakson of Georgia, would promote research that uses embryos that are “naturally” dead or stem cells derived from alternate means. “What we offer here, we hope, is a third way,” Coleman said. “It avoids the culture wars. It moves the ball forward on research.”

Harkin disagreed, saying the Coleman-Isakson bill would have little effect on research. “I have no problems with it, but it doesn’t really do anything we can’t already do,” he said. Asked whether he would support it, Harkin held his nose and said, “I’ll vote ‘yea.’ ”

The Senate embryonic stem cell bill has been modified and is no longer identical to the House legislation. It includes language from a bill sponsored last year by Arlen Specter, R-Pa., and former Sen. Rick Santorum, R-Pa. (House, 1991-95; Senate, 1995-2007), promoting the further use of non-embryonic stem cells derived from adults.

Alex Wayne contributed to this story.

First posted April 10, 2007 1:12 p.m.