WASHINGTON -- President Bush rejected legislation Wednesday that could have multiplied the federal money going into embryonic stem cell research, using the first veto of his presidency to underscore his stand on the emotionally charged, life-and-death issue.

A few hours later, the House voted 235-193 to overturn the Bush's veto, 51 short of the required two-thirds majority.

"This bill would support the taking of innocent human life in the hope of finding medical benefits for others," Bush said. "It crosses a moral boundary that our decent society needs to respect."

Most Americans disagree with the president, according to public opinion polls. A number of lawmakers expressed confidence the legislation would someday become law and some suggested Bush's stance could hurt Republicans in congressional elections this fall.

"Mr. President, we will not give up," said Sen. Edward Kennedy, D-Mass. "We will continue this battle."

Bush made good on a promise he made in 2001 to limit federally funded embryonic research to the stem cell lines that had been created by the time.

Bush's first veto, 5 1/2 years into his presidency, came in the Oval Office without any ceremony -- though he then announced it surrounded by families with cheerful toddlers born from embryos. He added his signature to the bottom of a two-page message that was promptly hand-delivered to the House, where the legislation began.

"If we are to find the right ways to advance ethical medical research, we must also be willing when necessary to reject the wrong ways," his message said. "For that reason, I must veto this bill."

Bush has made 141 veto threats during his time in office, and the Republicans controlling Congress typically respond by changing bills to his liking. His single veto is a departure from the practices of other recent presidents -- Bill Clinton had 37, Bush's father had 44 and Ronald Reagan had 78.

Supporters of embryonic stem cell research have had powerfully moving proponents on their side, including the late "Superman" star Christopher Reeve and actor Michael J. Fox. Other proponents say the research could lead to cures for the diseases that threaten to kill them.

Bush tried to put a face on his position, too. Eighteen families who had adopted unused frozen embryos were in the East Room as Bush made his case in a 15-minute speech that came 40 minutes after the veto. On stage behind the president and in the audience were two dozen children, squirming in their Sunday best, born from those leftover embryos.

"These boys and girls are not spare parts," Bush said. "They remind us of what is lost when embryos are destroyed in the name of research."

Also in the crowd were four embryo donor families and four patients who have been aided by adult stem cells. Those cells are found in various tissues, including bone marrow. Bush supports research involving adult stem cells.

As he vetoed the bill, he signed another that was passed unanimously in both chambers that would ban "fetal farming," the prospect of raising and aborting fetuses for scientific research.

"Human beings are not a raw material to be exploited, or a commodity to be bought or sold, and this bill will help ensure that we respect the fundamental ethical line," Bush said, drawing a shout of "Amen!" from one of the fathers on stage with him.

Bush said he was disappointed that Congress failed to pass a third bill that would encourage adult stem cell research. Opponents said it would have given lawmakers political cover for opposing the embryonic stem cell bill. But Bush said it would fund vital and ethical research, and he would direct his administration to pursue this kind of science.

Pleadings from celebrities, former first lady Nancy Reagan and some fellow Republicans had failed to move Bush. He acted after two days of often wrenching emotional debate in Congress, punctuated by stories of personal and family suffering, that had cast lawmakers into the intersection of politics, morality and science.

Some are predicting the veto could hurt GOP congressional candidates in close races this November. And the issue split the Republican senators who are thinking about running to replace Bush in the White House in 2008.

Sens. Sam Brownback of Kansas, Chuck Hagel of Nebraska and George Allen of Virginia sided with Bush in opposing the bill. Senate Majority Leader Bill Frist of Tennessee and Sen. John McCain of Arizona voted for the increased federal funding.

"I am pro-life, but I disagree with the president's decision to veto the Stem Cell Research Enhancement Act," said Frist, a heart surgeon. "Given the potential of this research and the limitations of the existing lines eligible for federally funded research, I think additional lines should be made available."

Rep. Diana DeGette, D-Colo., a co-sponsor of the House bill, submitted 11,000 signatures urging Bush to sign the measure and said of his veto: "He is doing that on the backs of tens of millions of Americans."