Washington ? The U.S. House on Thursday overwhelmingly approved a bill that would loosen the restrictions on human embryonic stem cell research imposed by President Bush in 2001, inaugurating the second such assault on the administration’s stem cell policy in as many years.

Thirty-seven Republicans joined 216 Democrats to pass the Stem Cell Research Enhancement Act, which would allow federal funding of research on stem cells from embryos slated for destruction at fertility clinics.

The 253 to 174 vote fell 37 votes short of what it would take to override the veto that Bush on Thursday promised would be forthcoming, assuming the Senate passes the same bill, as expected. Bush vetoed the legislation after it passed last year.

But buoyant research proponents said they still have several options and promised to persevere until the legislation becomes law.

“While it’s not enough to override a veto, it’s enough to show we have tremendous momentum,” said Rep. Diana DeGette, D-Colo., who led the House effort with Rep. Michael Castle, R-Del.

With the Senate already within one vote of having the two-thirds majority it needs for an override, and with the Democrats now in a majority position that will allow them to use procedural rules in their favor, DeGette suggested that it is time for the president to begin negotiating with Congress over compromise language.

“The vote today shows that productive discussions might be a very, very good idea for all concerned,” she said.

Under the existing policy, federal funds may be used to study only those stem cells taken from embryos destroyed by Aug. 9, 2001 – or about 21 of the nearly 400 stem cell colonies created since 1998.

The House-based bill would expand that pool of available cells to include those from any of the thousands of embryos that are discarded by fertility clinics each year, as long as those cells were freely donated for research by the parents. It would also impose some of the country’s first ethics rules on embryo research.

The vote came after about three hours of impassioned speeches by members on both sides of the issue.

Rep. Roger Wicker, R-Miss., warned that passage would lead to a “slippery slope.” Before long, he said, scientists would routinely be creating human embryos “for the express purpose of killing that embryo” for research.

Rep. Roscoe Bartlett, R-Md., touting his credentials as a former research scientist who studied human embryology, spoke up for alternative methods of getting stem cells – methods that virtually all leading stem cell scientists have discounted as having uncertain value. “The assumption by many people that you have to kill human embryos to get embryonic stem cells just isn’t true,” Bartlett said.

On the other side, Rep. Edward Markey, D-Mass., warned that if Congress does not override a Bush veto this time, “this will be remembered as a Luddite Moment in American history, where fear triumphed over hope and ideology triumphed over science.”

Rep. Rahm Emanuel, D-Ill., wondered aloud – not seriously, he assured – whether those voting against the bill would be willing to waive their right to access the cures that would come from the work.

When the final vote was tallied, Speaker Nancy Pelosi, D-Calif., took to the podium and announced with apparent glee, “The bill is passed!”

Passage came into question only briefly when Rep. Michael Burgess, R-Texas, introduced a motion that would have amended the bill to include broad new limits on scientists’ ability to clone human embryos for research.

Scientists have said that cloned human embryos offer a unique opportunity to create stem cells with particular genetic defects, giving researchers an unprecedented window into the underpinnings of birth defects and a wide range of diseases.

Current federal policy already precludes the use of federal funds for such studies. But Burgess’ motion would have cut off all federal embryonic stem cell grant money for any laboratory where embryo cloning research was under way even with private money.

The motion was defeated 238 to 189 after a frantic effort by leaders in both parties.

Senate leaders have said that they plan to take up the bill next month.