WASHINGTON -- Ignoring a veto threat, the House moved Tuesday toward approving a bill loosening President George W. Bush's restrictions on stem cell research, with supporters claiming prospects were enhanced by promises that such research would offer new treatments for a host of debilitating ailments.

Bush was expected to speak on the issue at 2:10 p.m. EDT in the White House Rose Garden.

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Live Video: Bush Speaks On Bioethics (2:10 p.m. EDT / 11:10 a.m. PDT)

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The House floor debate was framed in starkly emotional terms, particularly by opponents of federal funding for embryonic stem cell research who liken the process to abortion because human embryos would be destroyed.

House Majority Leader Tom DeLay said that using leftover embryos from fertility clinics amounts to the "dismemberment of living, distinct human beings" because the embryos are destroyed during the research. Conservatives offered an alternative measure to encourage research using stem cells from umbilical cords.

Supporters of embryonic stem cell research tried to cast the debate in terms of the possible medical cures that could come from it. "For America to stand back because of a moral principle and not allow sound scientific research to proceed under the umbrella of the National Institute of Health, I think, is unconscionable," said Rep. Charlie Bass, R-N.H.

The bill would lift Bush's 2001 ban on funding research using stem cells from embryos harvested since 21001.

DeLay, a Texas Republican, called the debate "a necessary and important step in our national conversation about the kind of people we will be, in a world of ever more promising and ever more unnerving medical technology." He equated reducing the funding restrictions imposed by Bush to a "vote to fund with taxpayer dollars the dismemberment of living, distinct human beings for the purposes of medical experimentation."

Sponsors predicted the bill would garner the 218 votes needed to pass but fall short of the 290 votes needed to sustain a veto. One sponsor acknowledged the difficult choice facing lawmakers.

"This is not an easy vote for many Republicans ... and some Democrats, too, because you have pro-life and other arguments," said Rep. Mike Castle, R-Del. "There's a lot of tide against them voting for it."

Expecting House passage of that bill, its Senate sponsors, Arlen Specter, R-Pa., and Tom Harkin, D-Iowa, were drafting a letter to House Majority Leader Bill Frist of Tennessee urging quick passage in that chamber.

In the House, DeLay urged passage of a second bill, sponsored by Reps. Chris Smith, R-N.J. and Artur Davis, D-Ala., which would provide $79 million in federal money to increase the amount of umbilical cord blood for stem cell research and treatment and establish a national database for patients looking for matches.

Many lawmakers said they planned to vote for both stem cell research bills.

Away from the House floor, there were emotional appeals from survivors of disease who credit stem cell science with saving their lives.

Appearing on Capitol Hill and with Bush at the White House were the parents of babies "adopted" as embryos. They object to the Castle-DeGette bill's premise that embryonic stem cell research makes use of fertilized eggs that would otherwise be discarded.

Decrying science that destroys life to prolong other life, Bush last week promised to veto the Castle-DeGette bill, and some lawmakers were taking note.

Driving the debate over these bills was deep emotion behind the promise -- disputed in some camps -- that stem cell research could provide treatment and perhaps cures for diseases as diverse as Parkinson's, Alzheimer's and childhood diabetes.

"As you consider the funding options for stem cell research, please remember me," Keone Penn, 18, said at a Capitol Hill news conference. He said he had been stricken with childhood sickle cell anemia and cured after a transplant from umbilical cord blood.

Penn, of Atlanta, said sickle cell anemia caused a stroke when he was 5. Treatment for the disease was so painful that he said he contemplated suicide four years later. Doctors predicted he would not live to adulthood, but because of the transplant, he turns 19 in two weeks.

"If it wasn't for cord blood, I'd probably be dead by now," he said.

Blood saved from newborns' umbilical cords is rich in a type of stem cells that produce blood, the same kind that make up bone-marrow transplants. The Institute of Medicine recently estimated that cord blood could help treat about 11,700 Americans a year with leukemia and other devastating diseases, yet most is routinely discarded.

The Castle-DeGette bill deals with embryonic stem cells, which are the building blocks for every tissue in the body. Attempting to harness those stem cells' regenerative powers is in very early research stages, but many scientists believe it has the potential to one day create breakthrough treatments.