WASHINGTON - The addition of one word - "embryo" - to a federal advisory committee's charter not only provides subtle widening of the ethical debate over embryonic research, but it also could add further restrictions on clinical trials in the future.

The Bush administration has revised the charter of a federal advisory committee, first formed during the Clinton administration, to protect human subjects in research. The revision specifies that embryos used in research are "human subjects" whose welfare should be considered.

The embryo now joins the ranks of other groups, including fetuses, newborns, children, prisoners, adults and those with impaired decision-making ability requiring special protection in research.

Stricter rules over what is considered a human subject could mean additional delays in getting the green light for clinical trials, researchers said. Institutional review boards would have to approve any research involving embryos, should the revised definition ultimately get regulatory status, they said.

Specifically, the charter directs the committee to consider "pregnant women, embryos and fetuses." Members of the advisory committee have not been announced nor has an announcement about a new committee come from the U.S. Department of Health and Human Services.

The revision to the charter is not significant, according to HHS spokesman Bill Pierce. "For many people, the terms fetuses, embryos and unborn children are used to describe the same things," he said.

Fetuses already have limited federal protection. Prenatal care, for example, is now considered a "right" of the fetus. Embryos, that is, the cluster of cells that represent the earliest stages of human development, are showing promise in determining the causes of birth defects and infertility. Embryos also contain the controversial stem cells that hold clues to treating or curing degenerative diseases.

A majority of the existing embryo inventory isn't even viable to develop into a human fetus, according to statistics from the American Society for Reproductive Medicine in Birmingham, Ala. The group is concerned that the change in wording could become a regulatory nightmare for infertility clinics, it said in a statement.

"We do not think that an entity that is designed to protect human subjects of research is the appropriate place to deal with the regulation of reproductive tissues, be they sperm, eggs or embryos," said Sean Tipton, a spokesman for the group.

While the revised wording does not carry regulatory power to change federal policy, it does offer further evidence that the administration considers the rights of embryos and fetuses just as important as children and adults. Shortly after taking office, President Bush placed restrictions on federal funding of stem cell research by limiting it to a certain number of existing cell lines.

Federal funding for research that harms embryos is currently banned by Congress, but the ban requires an annual renewal, and its definition of embryo does not equate it with being a human subject.

The advisory committee will offer recommendations to HHS, and in turn the agency would have to begin the rulemaking process or seek legislation if it wanted additional protections in place. The committee was first created as the National Human Research Protections Advisory Committee, but the Bush administration let the charter expire in September. The new committee is called the Secretary's Advisory Committee on Human Research Protections.

The new committee's charter closely follows the departure of the director for the Office of Human Research Protections, Greg Koski, who, according to some in the research community, left because of philosophical differences in how the office should operate. The office was created to strengthen federal oversight of government-funded research, following several high-profile deaths of patients involved in clinical trial research.