The legislation would free up federal funds to conduct research on cells taken from human embryos, which are considered by scientists to be the most promising source of potential new treatments for spinal cord injuries and degenerative diseases including Alzheimer's, Parkinson's and cancer.
Bush last year vetoed a similar bill and limited federally funded research to 21 lines of embryonic cells created before 2001, some of which scientists say have been compromised or corrupted.
The Stem Cell Research Enhancement Act would pay for research on stem cells extracted only from embryos slated to be discarded by in vitro fertility clinics annually and only with the consent of the donors of those embryos. It sets up ethical and reporting guidelines.
"Diseases like diabetes, Alzheimer's and cancer wreak havoc on lives of millions of Americans. We can free our loved ones from this pain, but only if we free science to find the keys," Rep. Edward Markey (D-Mass.) said during the debate. "Embryonic stem cell research is the flickering candle of medical promise that gives hope for the treatment and cure of these devastating diseases. Please do not condemn the afflicted to another generation of darkness."
Opponents charge that it is immoral and unethical to fund research that involves destroying embryos.
In threatening a renewed veto, Bush said in a statement that the bill "would use federal taxpayer dollars to support and encourage the destruction of human life for research."
Sen. Tom Harkin (D-Iowa), a major backer of the measure, says he believes supporters have the 67 votes needed in the Senate to override a presidential veto.