Bush called the bill a mistake and said he would veto it. The House approved it by a 238-194 vote, far short of the two-thirds majority that would be needed to override a veto.

''This bill would take us across a critical ethical line by creating new incentives for the ongoing destruction of emerging human life,'' the president said Tuesday. ''Crossing this line would be a great mistake.''

An alternative offered by Republican leaders that would fund research using stem cells derived from adults and umbilical cords rather than from embryos, passed 430-1, with Rep. Ron Paul, R-Texas, the lone opponent. But the focus was on the embryo bill.

Majority Leader Tom DeLay, R-Texas, said the embryonic research bill would force taxpayers to finance ''the dismemberment of living, distinct human beings.''

The rhetoric didn't sway many Democrats.

''I don't need a lecture from the majority leader on moral and ethical leadership,'' said Rep. Pete Stark, D-Calif., referring to questions that have been raised about DeLay's travel, fundraising and associations with a lobbyist now under federal criminal investigation.

Supporters of the measure said many embryos that would be studied would otherwise be discarded rather than implanted in the wombs of surrogate mothers. The moral obligation, they argued, rested on Congress to fund research that could lead to cures for diseases like Parkinson's and Alzheimer's.

''Being pro-life also means fighting for policies that will eliminate pain and suffering,'' said Rep. James R. Langevin, D-R.I., who was paralyzed at 16 in a gun accident.

Many members voted for both measures, saying that together they represented hope for the largest number of people critically ill with diseases that scientists say could be treated or even cured through stem cell research.

To support only one measure, said Rep. Sherrod Brown, D-Ohio., would be to ''offer hope to some and sympathy to others.''

The more controversial bill, sponsored by Reps. Mike Castle, R-Del., and Diana DeGette, D-Colo., would lift Bush's 2001 ban on federal funding for new research using stem cells from embryos that had not been destroyed before August 2001.

The House vote on the Castle-DeGette bill was intended mostly as a show of force to help propel it through the Senate and, the sponsors hope, into compromise talks with the White House.

In the Senate, Arlen Specter, R-Pa. and Tom Harkin, D-Iowa, asked Senate Majority Leader Bill Frist, R-Tenn., to immediately bring the stem cell issue to the Senate floor. Backers of embryonic stem cell research said the measure was supported by 60 senators, enough to break a filibuster by opponents, and could even get a two-thirds majority that would be enough to overpower a presidential veto.

The House floor discussion often echoed the emotional terms of the abortion debate and Terri Schiavo's right-to-die case.

Rep. Michael Burgess, R-Texas, a doctor of obstetrics, played the sound of a fetal heartbeat over the House speaker system, declaring, ''This is what it's all about, folks.''

The bill favored by GOP leaders and Bush was widely supported by members of both parties. Sponsored by Reps. Chris Smith, R-N.J., and Artur Davis, D-Ala., it would provide $79 million to increase stem cell research using umbilical cord blood and establish a national database for patients looking for matches. It also would clear the way for studies on stem cells derived from adults.

The two address very different procedures.

Blood saved from newborns' umbilical cords is rich in a type of stem cells that produces blood in the same way that transplanted bone marrow produces it. 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.