So-called natural family planning has been around since before the begats.

In general, the term refers to the judicial use of abstinence or non-abstinence from sexual relations during certain periods of a woman's reproductive cycle to avert or enhance fertility.

It has had its voguish periods, and its champions, in recent decades primarily among Catholics proscribed from barrier contraception or the pill by religious considerations.

It has also had passionate critics -- warning of its poor success rates or of its susceptibility to accidents at the beginning or end of the period of astinence -- tending to fertilization of overaged eggs or by an overaged sperm and leading to a higher percentage of miscarriages or infants with serious or fatal birth defects.

Indeed, the so-called rhythem method was a hit-or-miss operation assuming not only that all women were alike, but that any given woman was the same, month after month.

It was no wonder its success rate was something less than impressive. (As one Maryland gynecologist puts it, "If you only make a mistake once a year, that means a baby a year. . . .")

Gradually, however, a series of social factors -- along with a series of independent medical observations -- began to form the pressures leading to a refinement of techniques for new kinds of natural family-planning systems. Some of the techniques derived from efforts to solve problems of infertility; the natural systems may generally be used both to prevent or to enhance conception.

These pressures came both from Catholics caught between a desire for greater control over family size and a commitment to their religious dictates and from feminists, some Catholic (and many not) seeking greater knowledge of and control over their own bodies.

And, of course, there were the side effects that began to be noticed with modern methods of contraception: the pill, the IUD, spermicides, all suspect in a number of afflictions, including cancer and birth defects.

And as natural anything began to take on new appeal scientific progress -- and, for some, relaxed sexual mores -- saw the old rhythm method replaced by an array of gynecological observations, and even periodic abstinence replaced occasionally by alternative sexual activities.

A major contributor to the body of natural techniques now beginning to be known as "fertility awareness" is Dr. Edward F. Keefe, a New York gynecologist. Sympathetic and full of humor, Keefe recounts how he discovered in the course of his practice that a woman's cervix changed position when she was ovulating, and how few of his colleagues expressed any but the most causal interest in this observation.

But with that and other observations, and those of colleagues regarding the cyclical changes in a woman's temperature, the cyclic thinning of the cervical mucosa and the softening of the cervix, Dr. Keefe helped develop a system called the Symptothermal Method. It is popular with feminist groups, in part because it gives a woman the fullest biological knowledge of herself, and it is the method of choice of the Couple to Couple League, an organization that teaches it. (Keefe also devised a basal body thermometer that is easier to read than the usual one and is geared to the temperature change at the time of ovulation.)

The Billings Method, which relies principally on the changes in the mucosa, was developed by a husband-wife doctor team in Australia and also is enjoying a currency, especially among Catholic groups.

Both methods and variations of them are relatively complicated, requiring charting of a number of menstrual and ovulatory cycles. Although there are books available, classes of motivated people are more likely to achieve success.

Dr. Hanna Klaus, a gynecologist in Bethesda who teaches the Billings Method and is using it in a Kennedy Foundation-sponsored study of adolescent fertility awareness, believes that it alone is sufficient and claims a success rate comparable to other modern methods.

Keefe believes Sympto-thermal has an edge in effciency, but concedes that, as with all things, "the method works for people motivated to use it."

A recent discussion of national family planning in a bulletin issued by the Population Crisis Committee lists these advantages to natural family planning:

Religious sanction for Catholics.

Absence of side effects. A method that is immediately reversible and virtually without cost, once learned.

Self-knowledge.

Marital cooperation. (Shared responsibility for deferred gratification also is considered a plus by the Couple to Couple League.)

The Committee warns, however, that the issue of birth defects has not been solved and that the enormous variability of women and their cycles makes widespread success questionable.

Nevertheless, other modern methods carry their own risks and women and their partners may find the natural method appealing, useful and successful.