WASHINGTON - Vetoing a stem cell bill for the second time, President Bush on Wednesday sought to placate those who disagree with him by signing an executive order urging scientists toward what he termed "ethically responsible" research in the field.

President Bush, left, accompanied by the McNamara family of Middletown, Conn., from second from left, spina bifida patient Kaitlyne McNamara, her parents Mike and Tracy McNamara, and brother Ian McNamara, right, makes remarks on stem cell research, Wednesday, June 20, 2007, in the East Room of the White House in Washington. [AP]

Bush announced no new federal dollars for stem cell research, which supporters say holds the promise of disease cures, and his order would not allow researchers to do anything they couldn't do under existing restrictions.

Announcing his veto to a roomful of supporters, Bush said, "If this legislation became law, it would compel American taxpayers for the first time in our history to support the deliberate destruction of human embryos. I made it clear to Congress and to the American people that I will not allow our nation to cross this moral line."

He vetoed similar embryonic stem cell legislation last July.

His executive order encourages scientists to work with the government to add other kinds of stem cell research to the list of projects eligible for federal funding - so long as it does not create, harm or destroy human embryos.

Democrats dismissed Bush's veto as a moral affront, and his executive order as a meaningless gesture meant to trick people into thinking he had advanced stem cell research. They said they would hold votes to try to override the veto - or at least give the issue more air time.

"We also intend to continue bringing this up until we have a pro-stem cell president and a pro-stem cell Congress," said one of the House's chief sponsors, Rep. Diana DeGette, D-Colo.

Senate Democrats were expected to begin the process by trying to add embryonic stem cell legislation this week to a must-pass appropriations bill for the Labor and Health and Human Services departments.

The provision, proposed by Sen. Tom Harkin, D-Iowa, would allow taxpayer dollars to be spent on research on human embryonic stem cell lines derived before June 15, 2007 - moving the date of Bush's ban on public funding for such research up by nearly six years. Research on stem cell lines derived in the interim would be eligible for federal funding. The new provision also would add ethical standards to be used for selecting embryos to be studied, according to a draft of the provision.

By the 2008 elections, Democrats predicted, Bush's veto of new public funding for embryonic stem cell research would be a top priority of voters in the congressional and presidential elections.

Public opinion polls show strong support for the research.

Republican presidential hopefuls are split on the scope of federal involvement in embryonic stem cell research. Sen. John McCain of Arizona and former New York Mayor Rudy Giuliani have broken with Bush - and the GOP's social conservatives - in backing the expansion of federal funding for such research. At the Republican debate on May 3, Giuliani said he supported such an expansion with limits, "as long as we're not creating life in order to destroy it, as long as we're not having human cloning."

Rivals Mitt Romney and Sen. Sam Brownback of Kansas oppose the expansion. As governor of Massachusetts, Romney tried to stop legislation that encouraged expanded embryonic stem cell research. His veto was overturned.

Most of the Democratic candidates have urged Bush to expand the research.

The president is "deferring the hopes of millions of Americans who do not have the time to keep waiting for the cure that may save or extend lives," said Democratic presidential hopeful Sen. Barack Obama of Illinois.

Sen. Hillary Clinton, D-N.Y., said if she is elected president, she will lift restrictions on stem cell research.

"This is just one example of how the president puts ideology before science, politics before the needs of our families," she said.

Scientists were first able to conduct research with embryonic stem cells in 1998, according to the National Institutes of Health. There were no federal funds available for the work until Bush announced on Aug. 9, 2001, that his administration would spend tax money for research on lines of cells that already were in existence.

Currently, states and private organizations are permitted to fund embryonic stem cell research, but federal support is limited to cells that existed as of Aug. 9, 2001. The latest bill was aimed at lifting that restriction.

Bush urged support of legislation sponsored by Sen. Norm Coleman, R-Minn., which passed the Senate but has not yet been taken up by the House. Coleman says his measure supports federal funding for embryonic stem cell research methods that do not harm embryos. "It provides for ethically responsible stem cell research sooner rather than later," Coleman said.

Bush said his executive order directs the Health and Human Services Department to promote research into cells that - like human embryonic stem cells - also hold the potential of regenerating into different types of cells that might be used to battle disease and make them eligible for federal funding.

The order also renames the NIH's Embryonic Stem Cell Registry the Pluripotent Stem Cell Registry so that it reflects what the stem cells can do, instead of their origin. Pluripotent stem cells are ones that can give rise to any kind of cell in the body except those required to develop a fetus.

"Destroying human life in the hopes of saving human life is not ethical, and it is not the only option before us," said Bush, who appeared on stage with Kaitlyne McNamara of Middletown, Conn., who was born with spina bifida, and is benefiting from what he called "ethical stem cell research."

Sean Tipton, president of the Coalition for the Advancement of Medical Research, expressed anger and disgust at the veto and Bush's order.

"His executive order directing NIH to continue pursing alternate forms of research is nothing new since NIH has already been conducting this research for the past 20 years," Tipton said.