As so often happens, another thing of the past is about to be the wave of the future.

This time it's the cervical cap.

As the controversy about use of the Pill continues to flare -- and a final verdict may be years away -- more and more women have found the growing indictment linking birth-control pills to circulatory problems and cancer enough reason to seek other means of contraception for self, or partners.

Reports, however, are burgeoning now about IUDs and their link to potentially sterilizing, even life-threatening infections, often (perhaps especially) after years of use. So, by and large, IUDs, too, have been all but eliminated as a viable option, women's health groups and many medical authorities believe.

In fact, the National Women's Health Network last month filed a suit against the A. H. Robins Co. to force a worldwide recall of their IUD, the Dalkan Shield. Its sales in this country were suspended in 1974 after it was linked to several deaths among American women, the suit claims, but it was never recalled.

Robins spokesman Roscoe Puckett says the company, which is "vigorously" contesting the suit, notes that Robins has recommended in a letter sent "to physicians, health-care authorities and family-planning groups in the U.S. and 70 other countries that "long-time users" of IUDs should have the devices removed. This would include any Dalkan Shield users, Puckett says, because it has not been marketed anywhere by Robins since 1975.

That leaves an assortment of mostly iffy rhythm methods, the condom, the irksome diaphragm-cum-spermacide -- and the cervical cap.

Barbara Seaman, perhaps the Pills's most implacable enemy in this country, virtually founded the women's health movement in this country with her book, "The Doctor's Case Against the Pill," first published 12 years ago and now updated (Doubleday-Dolphin, $6.50). She first discussed the cervical cap, and brought about a mini-revival of a method largely discarded in this country in the 1960s in favor of the diaphragm and Pill.

Feminist health groups, paraprofessionals, obstetric nurses, midwives and a few doctors began to fit women with caps purchased from the device's virtually exclusive manufacturer, Lamberts, Ltd, London. It became an underground feminist fad, but was largely obscured from the public eye.

The cap, usually a slightly pliable-to-rigid, bell-shaped, rubber or plastic device, fits snugly over the cervix. It was especially popular because, once in place, it could be left there for longer periods than the diaphragm, without the need for additional spermacidal foams or jellies, even as long as a week, some users believe. It had none of the risks of the Pill or IUD and was, the women felt, more effective than the diaphragm. It sells for aobut $6.

The cap requires skillful fitting, and is not appropriate for all women. Feminist clinicians, however, were painstaking and adroit, rejecting women for whom it would be ineffective, and patiently coaching others in its proper use. The New Hampshire Feminist Health Center in Concord and the Emma Goldman Clinic for Women in Iowa City, Ia., particularly became known for their successes and scrupulous technique and are still major sources for clinics and other cap providers throughout the country.

Then it came to the attention of the Food and Drug Administration.

It was the enactment of an amendment requiring FD approval for medical devices that put the FDA and the Women's Health groups at loggerheads.

The FDA stance, expressed by Dr. Lillian Yin, head of the division of gynecologic medical devices, was that the cap, although it had been used in its present form for years in Europe, had fallen into disfavor in this country for reasons not readily apparent and was therefore suspect. (Current cap-providers are convinced that it was simply a matter of inconvenience and time consumption to the doctors.) Lamberts, however, could neither produce formal, controlled studies as to the device's safety and efficacy nor show that it had been sold long enough in this country to warrant automatic FDA approval.

The feminist groups were confronted with the need for establishing scientific protocols, filing for investigational exemptions, finding or establishing institutional review boards and, they felt, overcoming a host of unnecessary bureaucratic obstacles. The FDA was adamant that no more exceptions could be made for the women's groups than for any manufacturer seeking approval for a device.

In any case, the decade of experience with the cap had proven to the women's satisfaction that it was the best currently available contraception for those women who could use it, and, with the New Hampshire group once more in the lead, are managing to meet FDA criteria.

NIH is also funding a three-yuear study on safety and efficacy.

The bottom line is this: Although the cervical cap, as manufactured (in varying sizes and in several types) by Lamberts is not yet approved for general distribution in this country by the FDA, enough investigational exemptions have been issued so that most women who wish to use it may be screened and fitted under one or another of the studies.

At a workshop sponsored Monday by the Washington Preterm clinic, about 25 ob-gyn physicians, nurses, midwives and others from the Washington Baltimore area gathered to hear experts on the cap explain its benefits and drawbacks (mainly the time required for fitting and instruction), to hear Dr. Yin explain the FDA position and requirements and to see techniques demonstrated for its use.

Among the most experienced participants were Sara Grusky and Laura Worby of Washington Women's Self Help, who hold periodic "Teach-Ins" for interested women where contraceptive methods are compared, followed by smaller meetings for fitting. The group has filed the required FDA forms and created its own institutional review board, but doesn't yet have its own office. The women may be reached daytimes at 387-4463 (Grusky) or 462-6863 (Worby.) Or by mail at P.O. Box 1604, Washington, D.C. 20013.

They are also willing to share their investigational protocol -- a procedure approved by Dr. Yin, so long as it is scrupulously followed once the FDA okays it. Successful investigational protocol also is available from the New Hampshire Center at 38 S. Main St. Concord, N.H. 03301. The latter has sent out more than 100 copies of their protocol, but must now charge $10 for copying and postage. (A similar amount should accompany requests from the Washington group.) The forms are complicated and lengthy and feminist health groups are, almost by their nature, shoestring operations dependent on volunteers and donations.

Other information may be obtained from Preterm, 1120 19th St. NW., Suite 200, Washington D.C. 20036, or from the National Women's Health Network, 224 7th St. SE, Washington D.C. 20003. Their information packet ($2.50) includes tips on the caps, as well as care and feeding of FDA and its rules, along with at least a partial llist of cap providers in this country. New Hampshire also has an information packet for $5.

The studies underway are designed to determine how long the cap may be wworn safely, if long-term use can affect the cervix, whether there are any other unanticipated side effects and if, indeed, they are effective barriers to contraception. And although there are no major U.S. cap manufacturers, there is developmental work being done on making them better -- including at least one to be custom-made for each user.