WASHINGTON - Scientists seeking potentially revolutionary breakthroughs in medicine through research with fetal stem cells faced a deadline Thursday to apply for funding from the National Institutes of Health.

Whether that money ever arrives is far less certain.

Opponents and supporters of the work break along the traditional fault lines of the abortion debate, with a few notable exceptions. Both sides have escalated their campaigns to influence the Bush administration's decision on whether to support the research, which involves removing stem cells from human embryos or fetal tissue.

``We're creating some huge moral problems in medicine and we need to look further down the line,'' said David Stevens, executive director of the Christian Medical Association, which opposes the work. ``You're creating a moral quandary in our country that we're going to be dealing with for years.''

The passion that the relatively new field of research stirs is a result of both its promise and its source.

Fetal stem cells are primordial cells that can develop into any of the tissues that form the body. That flexibility has encouraged scientists, doctors, biotech companies and patient-advocacy groups, who believe the cells could hold the key to groundbreaking treatments for diseases such as Alzheimer's, diabetes, spinal cord injury and heart disease.

The stem cells believed by many to offer the most promise, though, are taken from human embryos or the tissue of aborted fetuses, raising legal and ethical challenges for scientists seeking to do the research.

Congress has banned federally funded embryo research since 1995. But after a series of breakthroughs, the National Institutes of Health issued new rules last August allowing federally funded research on stem cells removed from the tens of thousands of fertilized eggs left behind at private fertility clinics. The key was that no federal money would be used to extract the cells, a procedure that destroys the embryo.

The NIH has set the deadline for grant applications.

President Bush has come out against the research, although his secretary of health and human services, Tommy Thompson, has supported the work in the past. (Thompson, a former governor of Wisconsin, praised the University of Wisconsin scientist who, in 1998, first isolated and grew stem cells from leftover embryos donated by couples at infertility clinics.)

Since taking office, Thompson has said that the NIH policy is under review and that a decision may take months. But he made clear that he was uneasy with the congressional restrictions on the research.

``There is a law on the books that is troublesome,'' he told the Senate Budget Committee in testimony last week.

The uncertainty of federal support has mobilized both sides.

The Christian Medical Association and a California adoption agency have filed a lawsuit in the US District Court for the District of Columbia to block the NIH funding. Thompson and Ruth Kirschstein, the acting director of the NIH, which falls under Thompson's authority, were named as defendants.

``Funding of embryo research is unnecessary, it's unlawful and it's immoral because we're taking another person's life,'' Stevens said. ``As far as Tommy Thompson is concerned, I'm not sure where he's coming from. I hope this suit will nudge him in the right direction.''

Earlier this month, the American Association for the Advancement of Science sent a letter to Bush expressing its support for the research. Citing the potential to help millions of people, the group said the work could prove to be the biggest scientific and medical breakthrough in the past decade.

Although opponents argue that adult stem cells may hold similar promise, the letter argued that they may be less effective than the fetal counterpart.

The letter followed a similar one by 80 Nobel Prize winners, urging Bush to continue to fund the studies. Their letter pointed out that the cells to be used in the research would be destroyed in any case.

The issue could prove contentious in Congress, too, although some Republicans have joined Democrats in backing the research.

A resolution introduced by Representatives Carolyn B. Maloney, Democrat of New York, and Constance A. Morella, Republican of Maryland, called the research essential and argued that federal funding ensured the work would be conducted according to ``the highest scientific and ethical standards.''

``It is my sincere hope that politically motivated lawsuits will not stand in the way of groundbreaking research,'' Maloney said.

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