Sitting in their clinic beds, their faces wincing with pain, two women from the London suburbs quietly waited for their pregnancies to be destroyed. They had taken the revolutionary French abortion pill known as RU-486 - a drug that could be available in U.S. clinics and doctors' offices by early next year.

The two women - both in their 30s, both with two children, and both emphatic about not wanting a third right now - are among thousands of European women choosing the drug because it allows them to avoid an invasive surgical abortion and general anesthetic.

But as the hours ticked away behind the flowered curtains of the Marie Stopes Fairfield Clinic here, the downside of the RU-486 method became more apparent. Such negatives may also hamper the drug's acceptance in the United States.

There was pain, considerable pain, something the two women described as worse than bad menstrual cramping and a bit closer to labor. They chose not to take painkillers.

There was inconvenience. Unlike two-visit surgical abortions, the RU-486 method requires at least three and sometimes four visits. One women at the clinic would miss a computer class, and the other would interrupt what should have been a honeymoon with a new husband.

There was uncertainty as well for the women, who agreed to be interviewed if their names were not published.

``A lot of women had the idea that using RU-486 was much simpler than it was,'' said Ann Furedi of Britain's Birth Control Trust, a reproductive-rights advisory group. They thought ``it was a matter of taking a couple of tablets and that would bring on your period and that was the end of it.''

In about 4 to 5 percent of cases, according to a researcher for the World Health Organization, RU-486 fails. After nearly eight hours of frustrated waiting, one of the two women would walk out of the Marie Stopes clinic still cramping and still pregnant, possibly facing a mop-up surgical abortion procedure she had tried all along to avoid.

In the case of the other woman, RU-486 worked perfectly. But even so, she didn't give it high marks. On a scale of 10, said the 31-year-old woman, ``I'd give it a 5 or 6 - I think it would be very frightening for a young person who hasn't had a baby; it is very painful.''

Still, the woman added, she preferred it over surgical abortion: ``This way is a lot easier.''

When it was introduced in France in 1988 by the pharmaceutical company Roussel Uclaf, the abortion pill raised a storm of controversy. Antiabortionists around the world warned that the drug would be dangerous. Inwardly they worried that it would make abortion much more popular - and less vulnerable to public attack - because it would allow women to simply take a pill and abort their pregnancies privately.

In fact, this was an original hope of the researchers who developed RU-486: that for the first time in human history, women would be able to take an ``abortion pill'' that would allow them to stop early pregnancies effectively, safely, quickly, painlessly and discreetly. Surgical abortion procedures would largely become a thing of the past.,

After years of use in Europe, however, the abortion pill has not met those expectations. While highly effective and safe - only one patient, a Frenchwoman with a poor health history, died using the method - it has not revolutionized abortion in Europe. Most abortion patients are still using surgical procedures. Those who choose RU-486 are encountering a highly medicalized procedure with its own drawbacks.

In France, the European country where the method is the most popular, about 25 percent of abortion patients choose RU-486. In Sweden, the figure is about 19 percent. The usage is lowest in Britain, where only about 12,000 of 180,000 annual abortions - roughly 6 percent - use RU-486, which in Europe goes under the brand name Mifegyne.

Some of that lagging usage is due to local medical customs and restraints. In France, women are allowed to use the drug only within 49 days of their last menstrual period - the same length of time that will be adhered to in the United States once the drug wins expected approval from the FDA.

In Britain, women wanting abortions first must get approval from two doctors. Those using the national health plan must often wait several weeks before they are referred to a clinic or hospital for the procedure. By then, many may be beyond the 63-day British limit for using the method.

Also, most European women opt for surgical abortions under general anesthetic, which makes the contrast with the painful RU-486 method all the more stark. In America, pain may be less of an issue: Most early surgical abortions are painful because they are done under a local anesthetic.

Some believe that RU-486 will become more popular in Europe as time goes on. Introduced to Britain just four years ago, its use is increasing by 20 to 24 percent a year, said Tony Eaton, United Kingdom spokesman for Hoechst Marion Roussel, which now owns RU-486. ``As we said, it would be a slow but steady increase,'' said Eaton.

As more doctors become educated about the method, RU-486 use is increasing in Sweden, which introduced the method in 1993, said Ketty Gunnerholm, Hoechst Marion Roussel's RU-486 product manager in Sweden. It's ``not a question of is this a better method,'' she said, ``but it's a question of a woman having a choice. ''

In France, said Roussel Uclaf spokeswoman Catherine Euvrard, ``we have the feeling that we have reached a plateau'' with RU-486. Many women avoid it because ``when they take a pill, they have the feeling they are truly responsible for the abortion. . . . [There can be more] psychological pain.''

In fact, women take not only the RU-486 tablets - which block the body's use of the hormone progesterone, necessary to maintain pregnancy - but often a prostaglandin as well.

It's the prostaglandin that finishes off the pregnancy, causing the painful uterine contractions that expel fetal tissue; without it, studies have shown, RU-486 works only about 85 percent of the time.

Because of the need for a prostaglandin, European RU-486 users face at least three visits to the doctor, and this will also be true in the United States. The first visit is to receive the drug; the second - lasting several hours - is to receive the prostaglandin and be observed by medical personnel while the abortion takes place; the third is to get a post-abortion assessment.

``Some women, especially working women, say that [three visits] is too inconvenient for them,'' said Liz Davis, manager of the Marie Stopes clinic here.

Out of about 800 women undergoing abortions at the Marie Stopes clinic each month, only about a dozen women opt for RU-486. On a recent Wednesday this month, just two out of 35 abortion patients - the two women mentioned at the beginning - were using it.

One of the two, a 38-year-old student whose boyfriend left her when he learned she was pregnant, would spend eight frustrating hours at the clinic, waiting for the expulsion of blood and rudimentary fetal tissue that would signal that her abortion was complete. As her cramps grew stronger, the woman - slim, pretty and black-haired - tried running up and down the clinic's stairs and jogging in place, to no avail.

``Always the awkward one,'' she said wryly to a clinic nurse, who sent her home with instructions to call in if she experienced heavy bleeding. If the RU-486 and prostaglandin didn't work within 24 hours, the woman faced a surgical procedure. Because of possible damage to the fetus, women are told that if the RU-486 fails, they have no choice but to end their pregnancies surgically. (The woman in fact aborted after she left the clinic, and did not need surgery.)

The woman's clinic companion, a recently married 31-year-old mother of two, was a textbook case of a successful RU-486 abortion. On Monday, 7 1/2 weeks pregnant, she swallowed three RU-486 tablets at the clinic. There was a slight amount of bleeding on Tuesday, followed by lower back pain Tuesday night.

On Wednesday morning she reported back to the clinic to receive prostaglandin in vaginal suppository form. About six hours later, grim-faced with pain, she went into a clinic bathroom and expelled two globs of blood about an inch and a half in diameter into a plastic pan.

Inspecting the tissue, clinic workers concluded that the abortion was complete. But the woman would have to return to the clinic for a final assessment.

Seeing the expelled pregnancy, she had no qualms about what she had done. ``I felt relief,'' she said. ``Is that what causes all that pain?''