President Bush says he will veto legislation that would relax restrictions on embryonic stem cell research. There is growing bipartisan support in Congress for changing those rules.
President Bush says he will not allow legislators to roll back limits on stem cell research he set in 2001.
"I've made very clear to the Congress that the use of federal money, taxpayers' money, to promote science which destroys life in order to save life, I'm against that. And therefore if the bill does that, I will veto it," Mr. Bush said.
Four years ago, President Bush restricted federal funding for embryonic stem cell research to a limited number of existing stem cell lines.
Supporters of legislation to expand that number say it could help develop treatments for diseases like Alzheimer's. Bipartisan backers of the bill are hoping for a vote in the House of Representatives next week.
White House officials say the president is not opposed to all stem cell research, just the creation of new embryonic lines which result in the death of a fetus.
That makes it a highly divisive issue in a nation where the political fight over abortion is still intense.
Some prominent Republicans, including former First Lady Nancy Reagan, have called on President Bush to ease restrictions on federal funding for more embryonic stem cell lines. Former President Ronald Reagan died last year after a long battle with Alzheimer's. His son, Ron Jr., made stem cells an issue in last year's presidential campaign with a speech at the Democratic National Convention.