WASHINGTON - Congress is facing mounting calls from some unexpected quarters to halt medical research involving human cloning.

Since the US House approved a ban on both reproductive and therapeutic cloning last summer, the dynamic in the nation's capital has changed from one that pitted religious conservatives and antiabortion groups against scientists, biotechnology firms, and patient advocates. Now some environmentalists, feminists, and other activists are joining social conservatives in calling on lawmakers to put the laboratory work on hold.

A broad coalition of biologists, ethicists, public-health advocates, abortion proponents, and human-rights activists signed a letter to leaders of the US Senate this week, urging a total ban on cloning to make babies and an indefinite moratorium on the creation of cloned embryos for use in medical research.

''Human cloning could be a gateway to a frightening new kind of eugenics, where discrimination and inequality are permanently written into our genetic code,'' said Marcy Darnovsky, a spokeswoman for the Center for Genetics and Society, a group based in Oakland, Calif., that organized the 100 signers and produced the letter.

In the Senate, lobbying is intense on the cloning issue. Senate majority leader Thomas A. Daschle, Democrat of South Dakota, has indicated that he will schedule a debate on cloning legislation in April or May.

One bill - sponsored by Senator Sam Brownback, Republican of Kansas - would ban and criminalize all human cloning. Senators Edward M. Kennedy, Democrat of Massachusetts, and Dianne Feinstein, Democrat of California, have introduced a separate measure banning reproductive cloning but allowing biomedical research with cloned embryos.

None of the cloning bills pending in the Senate would impose a moratorium on research. But both the Biotechnology Industry Organization, which represents 1,100 companies and research institutions, and the Coalition for the Advancement of Medical Research, made up of disease-research foundations and universities, are working feverishly to prevent the idea from catching fire.

Before research proceeds, the health risks posed to women in producing and harvesting the many eggs required for embryonic cloning needs to be addressed, perhaps through federal regulation, Judy Norsigian, founder of the Boston Women's Health Book Collective, told a Senate committee recently.

Norsigian and more than 100 women's health advocates have signed a statement calling for a ban on reproductive cloning and a five-year moratorium on embryonic cloning for medical research.

''This has nothing to do with the moral status of the embryo,'' said Norsigian, asserting that she is not aligned with antiabortion groups or the Roman Catholic Church, which condemn therapeutic cloning as the destruction of human life. ''I don't believe we have enough good data to go forward with the large-scale participation of women in harvesting eggs for stem-cell research.''

In November, Advanced Cell Technology of Worcester said it had created the first cloned human embryo by inserting adult DNA into a donated, hollowed-out egg. Medical researchers hope to harvest stem cells from these early embryos and produce healthy tissue to treat a variety of medical conditions, such as Parkinson's disease and juvenile diabetes.

The announcement by the Worcester firm alarmed some groups and individuals who suddenly saw human cloning as a here-and-now technology with the potential for genetic engineering of human beings.

''The problem with therapeutic cloning is that it introduces commercial eugenics from the get-go,'' said Jeremy Rifkin, a frequent critic of the biotechnology industry who heads the Foundation on Economic Trends in Washington.

''These new companies aim to control human reproduction from conception to birth, and that raises tremendous social issues about who holds the patent on life, who owns life,'' said Rifkin, who supports the Brownback bill to ban all cloning.

Leaders of several environmental groups, including Friends of the Earth, Greenpeace, and the Sierra Club signed the letter backing a moratorium on research cloning.

So has the president of the American Association of People with Disabilities, the executive director of Physicians for Human Rights, and the head of both the National Latina Health Organization and the California Black Women's Health Project.

''Dangling cures for a host of diseases, [Advanced Cell Technology] and others who will surely follow in their wake seek to throw open a Pandora's box of technologies that could easily do more harm than good,'' said Brent Blackwelder, president of Friends of the Earth.

''We have to have some regard for the consequences of our actions before we carry them out,'' he said.

Almost all senators are expected to support a ban on reproductive cloning.

But more than 20 senators remain undecided on the therapeutic-cloning issue, according to Daniel Perry, executive director of the Alliance for Aging Research.

''No senator wants to have the blood on their hands of saying `no' to medical research,'' Perry said. ''So this idea of a moratorium is a back door way to say we aren't going to criminalize research cloning, but we are going to put it on hold indefinitely. From the point of view of a girl with diabetes, it is really unacceptable to ask her to wait 5 or 10 years for research to proceed.''

Brownback, Kennedy, and Feinstein have rejected the idea of a research moratorium.

President Bush had said he wants a human-cloning ban but is awaiting a report on the medical and moral implications from his bioethics council this summer.

Michael Werner, vice president for bioethics at the Biotechnology Industry Organization, said the industry organization will probably begin running ads to ''put a human face on this research and its potential.''

Werner said his organizatoin could support a ban on reproductive cloning but not on research.

''A moratorium on research is a ban on research, and that it is not a compromise to us,'' he said.