After 12 years of studies in male rabbits, rats and rhesus monkeys, a Johns Hopkins University scientist has asked the Food and Drug Administration to approve human trials of a male contraceptive cream that is rubbed on the abdomen and chest.

Dr. Larry L. Ewing said that the contraceptive has sterilized its subjects temporarily in all its trials.

Ewing's proposed male contraceptive combines testosterone, the male sex hormone, with estradiol or estrogen, the main female sex hormone. Rubbing them directly into the skin is expected to be a highly efficient way of getting effective doses directly into the bloodstream.

In combination, Ewing and his colleagues have discovered, testosterone and estradiol powerfully suppress the production of a pituitary gland hormone that ordinarily stimulates the testes to produce the body's own testosterone.

The lack of this testosterone inhibits sperm production. But enough of the male sex hormone salve is left in the bloodstream to maintain male sex drive and potency.

Ewing described his research at a meeting of the Society for the Study of Reproduction at Case Western Reserve University in Cleveland last week.

In an interview, Dr. D.J. Patanelli of the National Institutes of Health's contraceptive development branch said no other formula so far has been able to sufficiently suppress spermatogenesis, formation of sperm cells in experimental animals.

Dr. Gabriel Bialy, chief of that branch, part of NIH's National Institute of Child Health and Human Development, was more cautious. Ewing's formula has not turned off sperm production completely, he said.

Still, he added, there have been no successful matings by males given the compound, "and I certainly think the contraceptive ought to be tried." Even if a male contraceptive had a failure rate of a few percent, he said, "it could still be acceptable" because even the birth control pill, the most effective female contracepive, has a small failure rate.

Ewing is a professor of reproductive biology who has been studying the regulation of testosterone production for 25 years. He began research on a possible male contraceptive 12 years ago, and the testosterone-estradiol formula he eventually developed was implanted under the skin of animals in sustained-released doses.

He said he used implants rather than pills partly for long-lasting effect, but in larger part because there is no safe, orally effective form of the male hormone that would not be broken down and changed in the gastrointestinal tract if taken orally.

The implants worked in animals, but to work in the human body an implant would be too big, hence the plan to use a salve to be rubbed daily into the upper abdomen and lower chest, two convenient, absorbent places.

Ewing said he hopes for FDA approval "within six months or a year" of a trial on human volunteeers in collaboration with Dr. Richard Sherins of NIH.

The first trial would seek to establish safe, effective dose levels. A test of safety and effectiveness in comparison with other methods would have to occur later, and general use could be years away, even "if we overcome all the stumbling blocks," Ewing said.