Pregnant less than a month, Marie Head called a clinic seeking an abortion and was given a choice: wait several weeks for the surgical procedure or take a new drug called mifepristone, then being offered by the clinic on an experimental basis.

Also known as RU-486, mifepristone is a synthetic steroid that makes it difficult for a fertilized egg to adhere to the uterus' lining. When it is taken with misoprostol, a drug that triggers uterine contractions, the result is an abortion.

Because the two-drug combination is not surgically invasive, it is sometimes called a "medical abortion."

Head, a federal employee in Atlanta, opted to try mifepristone. Her pregnancy was over within days. "I didn't want to have to wait and go through the emotional trauma and being nauseous {from morning sickness} and having to deal with that for four or five weeks," recalled Head, who compared taking RU-486 with having "a natural miscarriage."

The drug, which has been used by more than 200,000 women in Europe and China since 1988, has received tentative approval from U.S. health officials. Its introduction in the United States would offer women and physicians a new approach to abortion that would require a major public education campaign to be correctly understood, its proponents say.

On one hand, a "medical abortion" is a less invasive, nonsurgical process for terminating pregnancy that does not require anesthesia and can be used in the early days of pregnancy.

But the proper use of mifepristone requires three visits to a physician or clinic over a period of about 15 days. This regimen contrasts with the one-step surgical procedure that is very often done during a woman's first visit to a medical facility.

Also, the side effects of a "medical abortion" can include extensive bleeding, cramping, nausea and vomiting. On average, women experience varying degrees of bleeding for eight to nine days after a "medical abortion," compared with five days after a surgical abortion, according to information provided by the nonprofit Population Council, the drug's U.S. sponsor.

Most adverse side effects are caused by the second drug, misoprostol, which is sold under the brand name Cytotec and is already used to treat ulcers.

Mifepristone is most effective in the first 49 days of a pregnancy, but it can be safely used up to the 63rd day. After that, the drug becomes less effective and the side effects are more severe, according to clinical studies in France.

By contrast, surgical abortion is most effective and most often done later in pregnancy. Most clinicians are reluctant to do it before the eighth week because the fetus is so small -- at 63 days it is about two-thirds of an inch long -- that it can be missed during the procedure, which forces the embryo out of the uterus with a suction device. Legal Battle

In 1994, the French manufacturer of mifepristone gave its U.S. patent rights to the New York-based Population Council, which is working to bring the drug to market in this country. The Food and Drug Administration classified mifepristone as a "priority drug" and in September issued an "approvable letter," basically a conditional approval saying the drug was safe and effective. The drug regulators, however, asked for more information on its manufacturing and labeling before finally signing off on the drug.

The council says it hopes to obtain final approval and make the drug available by the end of this year. But that timetable is likely to slip because of a legal dispute between the council and Joseph D. Pike, the businessman it licensed to distribute and market mifepristone. The council, which contends that Pike defrauded it by not disclosing that he is a disbarred lawyer, is seeking his removal from the marketing project. Pike, who says his legal past is irrelevant to the business venture, has been reluctant to surrender full control. A trial in that lawsuit is set for March 31 in U.S. District Court in New York .

Antiabortion groups are opposed to the introduction of mifepristone in the United States and say its possible harmful effects on women have not yet been adequately assessed. Randall K. O'Bannon, director of research for the National Right to Life Committee, which opposes all forms of abortion, said its principal health concerns {about mifepristone} are extensive bleeding and changes in blood pressure. An American Protocol

Prior to seeking the FDA's approval of mifepristone, the Population Council submitted data from French tests of the drug and conducted its own clinical trials to test the drug's safety and effectiveness. The Atlanta clinic that Head called for her abortion was one of 17 sites around the country that took part in trials involving more than 2,100 women.

The council plans to present the final results of its trials at an academic conference sometime in early 1997, council spokeswoman Sandra Waldman said. Preliminary data presented to the FDA by the council last July showed that for the vast majority of the patients, mifepristone led to an effective abortion. But 82 percent of the women in the trial had painful contractions, generally after taking the second drug, misoprostol. Most, however, did not need to take painkillers.

Also, 26 women in the American study required hospitalization after the procedure and 32, or 1.5 percent, needed a follow-up suction abortion to stop bleeding because the drug procedure did not complete the job.

"There were no serious consequences to any patient, at least in our study," said Paul Blumenthal, associate professor of gynecology and obstetrics at Johns Hopkins University Medical School, who supervises another clinic that took part in the trials, the Johns Hopkins Baby Medical Center in Baltimore. About 50 women took mifepristone at that clinic, Blumenthal said.

The protocol used in the clinical trials is the one that will be taught to clinicians and physicians who want to use mifepristone when it becomes available, according to Anne Wilson, director of education and training at Advances in Health Technology Inc., a Washington-based nonprofit group set up by the council to educate the medical community and the public on the proper use of mifepristone.

That protocol recommends three visits to the physician or clinic providing mifepristone. During the first visit, medical workers verify that a woman is within the first 49 days of her pregnancy by asking her the date of her last menstrual period, doing a physical exam of the uterus or, if there is still doubt, doing a sonogram, Blumenthal said.

Clinicians also must determine whether the woman has any medical condition that would preclude the use of mifepristone, such as high blood pressure or a history of heart disease. Also, a woman taking a non-steroidal anti-inflammatory drug (NSAID), such as Motrin, for arthritis or cramps would have to stop that medication before a "medical abortion" because those drugs would inhibit the contraction-inducing effects of misoprostol, Blumenthal said.

Physicians will be urged to counsel patients during the first visit about how the drug works, its possible side effects and the necessity for two more visits. "This is really a regimen," Blumenthal said. "This is not a simple matter of one thing you do. . . . So patients who think they are not able to comply with returning for visits and taking the second medication on time are probably not good candidates."

Blumenthal said the extensive counseling and repeat visits may put off some physicians. "I think there are always going to be some physicians . . . that will say, Oh, I don't want to bother with this' because counseling and explaining are an integral part of the technique, of this method," he said.

If a patient wanted to proceed after being informed of what will be required, she would be given 600 milligrams of mifepristone tablets and sent home.

Two days later, she would return and take 400 micrograms of misoprostol to begin her contractions. Under the recommended protocol, women would be asked to remain at the clinic or doctor's office for four hours so they could be watched for complications and so the staff could confirm that the fetus was expelled.

About 54 percent of the women in French clinical studies expelled the embryo within four hours and another 22 percent within 24 hours. However, some women in mifepristone studies did not abort for longer periods, sometimes up to two weeks after taking misoprostol.

Head, who had her abortion in mid-1995, said that after she took misoprostol during her second visit to the clinic, she sat in a room with another woman and waited for the drug to work, talking, reading and watching television. "I had some very mild, mild cramping. I've had worse menstrual cramps," she said.

"I was passing tissues" that became progressively thicker, recalled Head, who appeared before an advisory panel convened by the FDA that recommended approval of the drug last July. About 3 1/2 hours after taking the drug, Head expelled the embryo, she said.

Some women may dislike this stage of a "medical abortion" because in contrast to a suction abortion, they have an opportunity to view the fetus. As Blumenthal noted, "one of the features of this kind of termination is that a patient may actually see the products of conception and may actually see the tiny, tiny fetus."

At the same time, other women may have the opposite problem. If they do not expel the embryo during the first four hours while in a clinical setting, they may not be able to confirm that they have passed it at home. Thus a woman can remain uncertain whether her abortion is completed until she makes her third visit, 12 to 14 days later.

During this third visit, the patient is checked for any side effects and medical staff confirm that the pregnancy is terminated. If there is any uncertainty about that, a pelvic exam or sonogram may be done.

If the pregnancy is not ended, "then a surgical abortion is highly recommended and should be done at that time," Advances in Health Technology's Wilson said. Limited Distribution Planned

A woman may decide to have a surgical abortion at any time after beginning a "medical abortion." But what if she changes her mind about having an abortion during the 48-hour period after she has taken mifepristone but before she has taken misoprostol?

The council said that it found only a few cases "where women decided to continue with their pregnancies after taking mifepristone to produce an abortion. In all but one case, a normal baby was delivered." In that one case, a sonogram indicated that the fetus had abnormalities and it was aborted surgically.

However, researchers do not yet have enough information to accurately predict how mifepristone would affect or damage a fetus that is not aborted, both Waldman and Wilson said. "There still needs to be more research, we feel, for what the outcome would be for a woman who continues her pregnancy," Wilson said.

As for misoprostol, there have been anecdotal reports of abnormal fetuses when pregnant women took the drug.

The council said it plans to distribute mifepristone only to physicians and will not make it available through pharmacies for at-home use.

It expects that a "medical abortion" will cost roughly the same as a surgical abortion. That procedure costs $300 to $350 when performed in a clinic; more when done in a hospital.

One of the attractions of mifepristone for some women -- and one of the reasons antiabortion groups disapprove of the drug -- is that it can be administered in a doctor's office and thus offers the possibility of greater privacy for both patients and physicians than outpatient surgical facilities do.

Whether mifepristone will lead to an increase in abortions is debated. Its proponents say it will not. "Anyone who has the impression that this is going to be a more rapid way of providing abortion, that is simply not the case," Wilson said. "I don't think this is going to increase the number of women who choose abortion, but it offers women an opportunity to better tailor the abortion procedure" to their preferences, she added. CAPTION: ABORTION PILL CHRONOLOGY 1970 Researchers discover the receptors within the uterine cells that interact with the hormone progesterone. 1980 Research team at Roussel Uclaf pharmaceutical company synthesizes a drug that fits into progesterone receptors, thus blocking the hormone needed to sustain pregnancy. The drug is labeled RU-486, or mifepristone. 1982 Roussel Uclaf reports a successful initial human testing of mifepristone to induce abortion and begins years of trials in several countries to test the drug in women less than seven weeks pregnant. 1983 The Population Council gets FDA approval to test mifepristone in the United States; during the next six years, more than 300 women receive mifepristone at the University of Southern California. 1984 A World Health Organization-sponsored study in Sweden shows success with a combination of mifepristone and a prostaglandin that provokes uterine contractions. 1988 The French Health Ministry announces approval of mifepristone combined with a prostaglandin for early medical abortion. But later in the year, Roussel Uclaf responds to protests from antiabortion groups and decides to suspend marketing mifepristone. The french health minister orders the drug back on the market two days later, calling it "the moral property of women." 1988 Mifepristone is approved in China. 1989 Mifepristone becomes available in France. 1991 Mifepristone is approved for use in the United Kingdom. 1992 Mifepristone is approved for use in Sweden. 1994 Roussel Uclaf gives the Population Council U.S. rights to mifepristone. The Population Council begins humanclinical trials of mifepristone in the United States. 1995 U.S. human trials end with 2,121 women having obtained mifepristone abortions. 1996 The Population Council applies to the FDA for approval of mifepristone in March. An FDA advisory committee recommends FDA approval in July. The FDA gives initial approval in September, asking for more information on manufacturing and labeling before giving final approval. CAPTION: HOW RU486 WORKS

Since 1988, RU-486, the abortion pill developed in France, has been used by more than 150,000 women in Europe to terminate pregnancies. Some advocate the drug as an important option for women who want to avoid surgery or who desire an abortion at a very early state of pregnancy before surgical abortion is medically feasible. 1. A woman's ovaries produce progesterone, a hormone that is necessary for fertilized eggs to implant and develop in the uterus. 2. RU-486 must be taken no later than the ninth week after the start of the last menstrual period. 3. The drug is an antiprogestin -- a synthetic agent that acts to block the effects of progesterone, causing the embryo's bond to the uterus to break down, halting fetal development. 4. Two days later, a second drug, prostaglandin, is taken. Prostaglandin is a synthetic hormone that causes the cervix to soften and dilate and the uterus to contract, expelling the fetus, usually within 4 hours.