The death of former President Ronald Reagan, after a lengthy battle with Alzheimer's disease, has refocused attention on research involving embryonic stem cells. The former president's widow has advocated stem cell research, which scientists hope can lead to progress in combating a number of diseases, including Alzheimer's.

Just weeks before Ronald Reagan's death, his wife, Nancy, spoke out on the need for more medical research involving stem cells obtained from human embryos that have been frozen. The frozen embryos would not, even if left intact, develop into babies.

"I just do not see how we can turn our backs on this," she said. "There are so many diseases that can be cured, or at least helped. We have lost so much time already, and I really cannot bear to lose anymore."

In a radio address Saturday, the presumed Democratic presidential nominee, Massachusetts Senator John Kerry, echoed Nancy Reagan's call. "Stem cells have the power to slow the loss of a grandmother's memory, calm the hand of an uncle with Parkinson's [disease], save a child from a lifetime of daily insulin shots, or permanently lift a best friend from his wheelchair," he said. "We must lift the barriers that stand in the way of science, and push the boundaries of medical exploration, so that researchers can find the cures that are there, if only they are allowed to look [for them]."

In 2001, President Bush signed an executive order limiting federal financing of stem cell research to several dozen stem cell lines that were available at the time. Officials said the idea was to allow research to go forward, without creating a financial incentive to harvest new embryos.

But new embryos are precisely what some researchers say they need to continue their work, and what many religious conservatives object to. Pat Dobson, founder of the group Focus on the Family, spoke on the CBS television program Face the Nation. "Science has always been governed by ethics," he said. "It has to be. It always has, except during the Nazi era, when as we know, unbelievable things occurred in concentration camps, because they were not governed by ethics. There have always been things we could have done, but do not do."

Fifty-eight U.S. senators and more than 200 House members have urged President Bush to relax federal restrictions on the use of stem cells. Pennsylvania Senator Arlen Specter is among those who signed a recent letter to the president. "What we need now is to have more stem cell lines available, because the ones authorized by President Bush are insufficient," he said.

Mr. Specter, who is chairman of the Health and Human Services Appropriations subcommittee, added that scientists need a free hand to combat disease.

President Bush has expressed deep reservations about destroying human embryos in order to further medical research.