WASHINGTON — President Obama's decision to lift restrictions on federal funding of human embryonic stem cell research, scheduled to be announced Monday, is expected to provide a major boost to one of the most promising but controversial fields of biomedical research in generations.

The signing of an executive order voiding the restrictions will allow thousands of scientists to study hundreds of lines of cells that have been developed since the limitations were put in place eight years ago.

It will also allow them to dismantle cumbersome bureaucracies and let them exchange scientific ideas more easily.

Because stem cells obtained from very early embryos are believed capable of morphing into any tissue in the body, scientists think they will lead to fundamental insights into the underlying causes of many diseases and repair damage caused by diabetes, Parkinson's disease, spinal cord injuries and other conditions — research backed by such notables as Nancy Reagan and the late Christopher Reeve.

But extracting the cells destroys the days-old embryos. In an effort to prevent tax dollars from encouraging the destruction of more embryos, President George W. Bush imposed the restriction on Aug. 9, 2001, limiting federal funding to studies of what turned out to be 21 cell lines that were already in existence as of that date.

"I feel vindicated after eight years of struggle, and I know it's going to energize my research team," said Dr. George Daley of the Harvard Stem Cell Institute and Children's Hospital of Boston, a leading stem cell researcher.

Critics have long complained that the cells that scientists have been permitted to study under the Bush policy have a variety of shortcomings. Many, for example, may have defects that could make them dangerous to transplant into people. But perhaps more importantly, hundreds of newer lines have been developed that offer a host of opportunities. Many lines, for example, carry defects for specific diseases and could yield crucial insights into how they develop and might be cured.

"This is huge," said Amy Comstock Rick of the Coalition for the Advancement of Medical Research, which lobbied to lift the restrictions. "It is eight years overdue to have human embryonic stem cell research put back in place with other forms of research for patients in this country."

Opponents, however, have argued that research on human embryonic stem cells has become unnecessary because of scientific advances in the interim, including promising studies involving adult stem cells and the ability to turn adult cells into cells that appear to have many of the properties of embryonic cells.

"Today's news that President Obama will open the door to direct taxpayer funds for embryonic stem cell research that encourages the destruction of human embryos is a slap in the face to Americans who believe in the dignity of all human life," said Tony Perkins of the Family Research Council. "It is unethical to use human life, even young embryonic life, to advance science.

"We should be increasing funding for adult stem cell treatments, which have been used to treat patients for over 70 diseases and conditions, and we should fund the historic achievements in reprogramming ordinary skin cells into embryonic-like stem cells without compromising ethics by destroying life," Perkins said.

But many scientists say it remains far from clear which cells will ultimately lead to the most important advances, making it crucial to continue to study embryonic cells along with other types.

NIH WILL TACKLE ETHICS

Obama made it clear during the campaign he would overturn Bush's directive, saying, "I strongly support expanding research on stem cells. I believe that the restrictions that President Bush has placed on funding of human embryonic stem cell research have handcuffed our scientists and hindered our ability to compete with other nations."

He had said he would lift Bush's ban and "ensure that all research on stem cells is conducted ethically and with rigorous oversight."

Some opponents have suggested that Obama might qualify his executive order to try to take the sting out of the move as part of his effort to find common ground on divisive issues. But those briefed on the content of the executive order yesterday said it would lift the restriction without caveats and let the NIH work out the details.

"This is what the patient community, the scientific community and the medical community has been asking for," said Lawrence Soler of the Juvenile Diabetes Research Foundation. "We need to give credit to the administration for living up their promise to keep politics out of science."

In anticipation of the decision, the NIH has started drafting guidelines that would address the many ethical issues raised by the research.

Unlike the low-key way Obama has reversed other Bush-era legacies related to culture war issues, the White House has invited scientists, advocates and members of Congress to a highly public ceremony for the signing.

Federal law would still prohibit using federal funds to actually destroy human embryos. But some scientists hope that federal funding will be allowed to support work on stem cells derived from a variety of sources, including from embryos specifically created to yield them, and not limited to those from frozen embryos destined to be discarded by infertility clinics.

"I don't personally have any problem creating embryos for embryonic stem cell research," said Mark Kay, a stem cell researcher at Stanford University. "But if he decides that embryos that have already been created and are going to be discarded are the ones that would be used, that would be reasonable as well. These things exist and are going to be discarded. It's really mind-boggling to me these things are going to be discarded and scientists haven't been allowed to use them to do research."