First Lady Laura Bush stepped into the debate over stem cell research today, defending her husband's policy restricting it against new Democratic criticism on the campaign trail.

Among the critics today was Democratic vice presidental nominee John Edwards, who marked the third anniversary of President Bush's August 2001 executive order limiting the research by charging that the administration has subordinated scientific advances to the dictates of conservative ideology.

"If we have a chance to make progress and cure diseases, if we have new medical breakthroughs that could improve millions of lives, then what's stopping us?" Edwards asked while campaigning in Illinois.

Speaking to the Pennsylvania Medical Society while campaigning for her husband, Laura Bush came to the defense of the administration's policy, which she characterized as taking into account both scientific and moral concerns.

"Although you might not know about it from listening to the news lately, the president also looks forward to medical breakthroughs that may arise from stem cell research," Laura Bush said. She said her husband "is the only president to ever authorize federal funding for embryonic stem cell research," for which the federal government last year spent $25 million, in addition to nearly $191 million on other stem cell research.

She said President Bush "has provided a boost to research in a very promising new field, while recognizing that this is an issue with moral implications that must not be treated lightly."

Her father died of Alzheimer's disease, and she hopes that stem cell research can help cure that and other illnesses, Laura Bush said.

"But I know that embryonic stem cell research is very preliminary right now, and the implication that cures for Alzheimer's are around the corner is just not right, and it's really not fair to the people who are watching a loved one suffer with this disease," she said.

Three years ago, Bush restricted federal funding for embryonic stem cell research to 78 stem cell lines then in existence. The cells form soon after conception and can be culled to replicate other tissues, potentially offering a cure for debilitating diseases. But some conservative religious groups oppose the research because harvesting the cells destroys the embryo.

In a radio address Saturday, Democratic presidential nominee John F. Kerry charged that Bush's decision has shut down "some of the most promising work to prevent, treat and cure Alzheimer's, Parkinson's, diabetes, AIDS and so many other life-threatening diseases."

Asserting that "right now, more than 100 million Americans suffer from illnesses that one day could be wiped away with stem-cell therapy," the Massachusetts senator accused Bush of sacrificing "science for ideology." Kerry called for making the funding of stem cell research a priority.

"People of good will and good sense can resolve the ethical issues without stopping life-saving research," Kerry said. He vowed that "help is on the way" to those waiting for cures that now seem beyond reach.

"I want you to hold on, and keep faith, because come next January, when John Edwards and I are sworn into office, we're going to create a new anniversary -- one that will be a cause for celebration," Kerry said. "We're going to lift the ban on stem cell research. We're going to listen to our scientists and stand up for science. We're going to say yes to knowledge, yes to discovery, and yes to a new era of hope for all Americans."

Addressing the issue in a press briefing today, White House spokesman Scott McClellan dodged questions on whether the president supports expanding research to additional cell lines, as advocated by a number of scientists and politicians from both parties.

The administration is proceeding "in a way that doesn't cross an ethical line," McClellan said, "and it's important that we not go down a dangerous, slippery slope where we divorce ethics from science."

He said the $24.8 million in federal funding for embryonic stem cell research in fiscal 2003 was "up from zero in the previous administration."

At the Democratic National Convention last month, Ron Reagan made an impassioned plea for stem cell research as a means of combating diseases such as Alzheimer's. The brain-wasting illness afflicted his father, former president Ronald Reagan, for a decade before he died in June. Former first lady Nancy Reagan has also called for expanding stem cell research.