WASHINGTON (AP) - President Bush sought to chart a compromise course Thursday night on an issue he called "one of the most profound of our time," endorsing scientific research on stem cells derived from human embryos - but only to a point.

"Embryonic stem cell research is at the leading edge of a series of moral hazards," the president said in a prime-time speech from his Texas ranch.

Political hazards, too, and his speech was replete with indications that he knew it.

He stressed the potential for breakthrough medical treatments. Yet he said stressed his belief that "human life is a sacred gift from our creator," and announced he would limit federal funding to cases in which embryos had already been destroyed.

He invoked the name of former President Reagan, afflicted with Alzheimer's disease, a hero still to a generation of conservatives who oppose abortion. Former first lady Nancy Reagan wrote him, Bush said, about her husband's struggle.

And he coupled his decision with an announcement that he would name conservative biomedical ethicist Leon Kass of the University of Chicago to a federal panel charged with monitoring the research.

Having settled the moral and ethical questions for his administration, Bush now must navigate the political hazards. Even before he spoke, some conservatives stood ready to attack him for violating a campaign pledge - a point the White House disputed energetically.

His speech seemed likely to fuel a gathering debate in Congress, too.

Strikingly, initial reaction was muted from lawmakers, from Democrats who said they wished he had gone further, and from Republicans who were plainly disappointed he went as far as he did.

House GOP Whip Tom DeLay of Texas said, mildly, that he was "disappointed" that Bush had opened the door to federal funding on stem cells derived from embryos that have already been destroyed. "I will continue working to educate a majority of Americans that we should always defend innocent life," he said.

Many congressional Democrats, equally mild, said they wished Bush had permitted scientists to create new sources of stem cells, a step that would mean the destruction of additional human embryos.

"On an issue such as this ... the Senate will want to take action," said Senate Majority Leader Tom Daschle, D-S.D. "President Bush's statement tonight puts us in a position to begin what I hope will be a constructive and bipartisan dialogue."

At issue was whether the government should support research on embryonic stem cells, harvested from embryos left over after fertility treatments. These are essentially blank-slate cells - and scientists see the possibility of using them to combat a variety of diseases such as Parkinson's and diabetes.

In his speech, Bush said federal funding could be used on stem cells derived from embryos that already have been destroyed, but that no additional embryos could be destroyed to further the scientific work.

In the hours before his speech, conservatives polished sharply worded press releases attacking the president of their own party, to be issued in the event he displeased them.

In the days leading up to it, members of Congress, including some abortion foes, and research advocates have spoken out in favor of federal funding to support the work.

First lady Laura Bush added her voice to the chorus recently when he said in an interview that the embryos at issue were created by infertile couples who now have all the children that they want.

"A lot of these embryos will be destroyed anyway or disposed of anyway, so I think that makes it even more difficult," she said on CNN's "Inside Politics" Monday. Asked about the opposition from those who oppose abortion rights, she said, "There's certainly a life side of it as well, when you think about life that could be saved by research."

Not surprisingly, Mrs. Bush stopped well short of lobbying her husband in public.

Not so Pope John Paul II, who lobbied Bush forcefully to oppose federal funding when the two men sat together in the Vatican a few weeks ago.

"A free and virtuous society, which America aspires to be, must reject practices that devalue and violate human life at any stage from conception to natural death," the pope said with Bush at his side.

"I'll take that point of view into consideration," the president replied respectfully.