President Bush vetoed an embryonic stem cell research funding bill Wednesday and called on Congress to put aside politics and support legislation that would advance science without crossing an ethical line.

“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," Bush said from the East Room of the White House, where he was joined by doctors and stem cell patients. "I made it clear to Congress and to the American people that I will not allow our nation to cross this moral line."

Bush's veto marks the third of his presidency and the second veto on a stem cell bill. Democrats don't have enough votes to override the veto. The vetoed bill would have eased restrictions on federal funding for stem cell research. Sources tell FOX News they expect an override vote in the coming weeks to fall just short of approval.

Alongside the veto, Bush issued an executive order on stem cell research to lay out the administration's position that it won't support new federal funding that would destroy embryos. The order will direct the Health and Human Services Department to conduct research into cells that could be used against deadly diseases.

Senate Majority Leader Harry Reid joined other Democrats in denouncing Bush's veto.

“He insists upon putting the politics of his narrow ideology ahead of saving lives. America deserves better,” Reid said on the Senate floor. “President Bush's veto is a setback in our fight, but nothing will stop the will of the American people to give you the hope that you deserve."

Senate Democrats might try to get another form of the stem cell bill through by attaching it to the annual labor appropriations bill, according to a report in the congressional newspaper, Roll Call.

Senate Democratic sources told Roll Call that Sens. Tom Harkin and Arlen Specter, the chairman and ranking member, respectively, of the Senate Appropriations subcommittee on Labor, Health and Human Services, Education and related agencies, agreed to tack the measure onto the fiscal 2008 spending bill for the departments of Labor and Health and Human Services.

That measure would expand stem cell lines available for federally funded research to include those derived before June 15, 2007 rather than the current cut-off date of Aug. 9, 2001. The bill would also tighten ethical guidelines on stem cell research.

On the House side, Rep. Rahm Emanuel, D-Ill., also lashed out at Bush's veto.

"The president formed his opinion on stem cell research and now he has America ensnarled in a political straightjacket," Emanuel said. "The American people see stem cell research as a cure to illnesses that plague their family and family members."

Bush needs to drop his veto threats and support life-saving stem cell research, said Rep. Michael Arcuri, D-N.Y.

"Stem cell research would give new hope to millions of Americans, families across the country suffering from life-threatening and debilitating diseases like Lupus, juvenile diabetes and Parkinson's," Arcuri said from the House floor before the president's veto.

House Minority Leader John Boehner released a statement of support for Bush's choice, saying Republicans have enough votes to sustain the veto.

"The president's veto today is justified for both moral and scientific reasons and it will be sustained by House Republicans," Boehner said.

Bush also won support from Republican senators who say other stem cell research is just as promising as embryonic stem cell research.

"Given the tremendous results that have come from adult and umbilical cord stem cell therapy in the areas of oncology and orthopedics — and, more recently, in cardiology and neurology — I am further encouraged by the possibilities these non-controversial, adult stem cells have to offer," said Sen. George Voinovich, R-Ohio.

"In this tight budgetary environment, in which there is a choke hold on our domestic discretionary spending, we must be vigilant in the way we appropriate taxpayer dollars and concentrate our resources on those lines of medical research that hold the greatest potential," he continued.

Sen. Hillary Clinton, a 2008 White House hopeful, told an audience at a forum of Democratic presidential contenders that the legislation the way it is written holds promises to fighting disease.

"Let me be very clear. When I am president, I will lift the ban on stem cell research," Clinton said at the "Take Back America" conference of liberal activists in Washington, D.C.

Clinton said Bush's veto shows the need for Democrats to win back the White House.

"This is just one example of how the president puts ideology before science, politics before the needs of our families, just one more example of how out of touch with reality he and his party have become," Clinton said.

Democratic leaders made the bill a priority when they took control of the House and the Senate in January. On Tuesday, House Speaker Nancy Pelosi sent out an e-mail letter asking for contributions to the Democratic Congressional Campaign Committee to help elect more Democrats so the bill could be passed in the future.

"By vetoing a bill that expands stem cell research, the president will say 'no' to the more than 70 percent of Americans who support it, 'no' to our Democratic Congress' fight for progress, and 'no' to saving lives and to potential cures for diseases such as diabetes and Parkinson's," Pelosi wrote. "He will say 'no' to hope."

Bush vetoed a similar measure last year that would allow funding of additional lines of embryonic stem cells. The third veto of his administration came on a bill that would require setting timetables for withdrawing U.S. troops from Iraq.

The National Institutes of Health says stem cells raise the prospect of a renewable source of replacement cells and tissues to treat Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns, heart disease, diabetes, osteoarthritis and rheumatoid arthritis and other conditions.

Scientists were first able to conduct research with embryonic stem cells in 1998, the NIH says. There were no federal funds for the work until Bush announced on Aug. 9, 2001, that his administration would make the funds available for 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 is aimed at lifting that restriction.

Public opinion polls show strong support for the research, and it could return as an issue in the 2008 presidential election.

The executive order Bush is signing will expand the NIH embryonic stem cell registry to include all types of "ethically produced" stem cells, the White House said. It also will encourage scientists to work with NIH to add new "ethically derived" stem cell lines to the list of those eligible for federal funding, based on new research coming forward.

Sen. Norm Coleman, R-Minn., has already proposed an alternative stem cell bill that passed the Senate.

"My stem cell bill, which passed the Senate with broad bipartisan support, offers a clear alternative for our colleagues in the House to significantly expand federally funded stem cell research, while ensuring no taxpayer dollars are used for the destruction of human embryos," Coleman said.

Bush said he would support funding for that measure or another proposed by Sen. Johnny Isakson, R-Ga.

FOX News' Trish Turner and Mike Emanuel and The Associated Press contributed to this report.