President George W. Bush said Tuesday that he would sign a bill to permit federal funding of research using human embryos that could not develop into fetuses.

At the same time, he said he would again reject a bill that would clear the way for the government to pay for largely unrestricted stem cell research on viable embryos. Bush's only veto in seven years as president was of a similar bill, which would have overturned a restrictive stem cell policy that Bush declared in 2001.

Both bills are moving toward a Senate vote this week with debate over budding science that many researchers say could cure diseases that afflict millions of people.

The bill Bush opposes, sponsored by Sen. Harry Reid, leader of the Senate's Democratic majority, would lift the president's ban on federal funding for any new embryonic stem cell studies.

Bush said Reid's measure crosses an ethical line because human embryos are destroyed in the process of extracting the stem cells, material that can morph into any tissue in the body and theoretically replace or heal damaged organs.

"The administration believes that research on alternative sources of stem cells is extremely promising and provides robust opportunities to advance science without compelling American taxpayers to participate in ongoing destruction of human embryos," the administration said in a statement.

If the measure passes both houses and reaches Bush's desk, "he would veto the bill," the statement said.

On the other hand, an alternative sponsored by Republican Sen. Johnny Isakson would stay on the ethical side of the debate by encouraging research that does not harm budding human life, the administration said in a separate statement. That measure would direct taxpayer money to stem cell research on fertilized embryos that had passed the window of time in which they are capable of developing into human beings.

"The administration does not believe science and ethics need be at odds," the statement said.

The bill also bans U.S. taxpayer money being spent on the creation of embryos for research purposes, a provision some scientists strongly oppose.