Homosexuality may be determined at birth by biology, according to a new study that indicates 10 percent of all children apparently are born with a strong "gender nonconformity" -- a failure to like the things other boys or girls like --that has nothing to do with upbringing and inevitably makes many of them homosexuals.

The study was made by the famed Kinsey Institute for Sex Research at Indiana University, where the late Dr. Alfred Kinsey made his revealing reports on male and female sexuality.

If the new study holds up, it could have equal impact. It rejects the traditional belief that homosexuality is generally caused by some early influence, that of a weak or a hostile father or a domineering or seductive mother or a traumatic sexual experience.

It maintains, instead, that homosexuality is usually, although not necessarily always, a deeply rooted trait present from infancy, and it well may be biological -- the result, perhaps, of an imbalance in sex hormones.

"We found homosexuality is deep-seated and not something that one chooses to be or not to be," said Dr. Alan Bell, senior author of the two-volume study to be published by Indiana University Press.

Homosexuality viewed as "the natural order" for some, he said, may necessitate far-reaching changes in law and in church doctrine, much of which views homosexuality as a crime or a sin, as well as in psychology, which views it as a product of family or society.

"If it's a basic hormonal thing," he said, the implication is that "one cannot legislate against a state over which a person has no control." Parents and society, he said, may have to recognize that trying to change homosexuals may be "swimming against their developmental history."

All these statements are certain to be challenged. Dr. William Masters and Virginia Johnson, the widely known sex research team of Masters and Johnson, said two years ago that a study of more than 300 homosexual men and women had convinced them that homosexuality is neither illness nor biochemical disorder, but rather a "learned behavior" that two out of three homosexuals can unlearn.

Psychiatrists have classically linked much homosexuality to unwitting parental influence.

"As hard as we tried," the usual theories "didn't work out," said Martin Weinberg of the Kinsey Institute.

The Indiana group, financed by the government's National Institute of Mental Health, interviewed 979 homosexuals and 477 heterosexuals or normally sexual persons in the San Francisco area in 1969 and 1970. Each was asked 200 questions in a five-hour interview.

The results, as the Indianans saw them:

* Homosexuality can't be traced back to any single psychological or social event or background but is a "very deeply rooted set of impulses and yearnings . . . needs and feelings."

* Heterosexuals -- but not homosexuals -- usually show early gender conformity. Boys throw balls, girls play with dolls. This is not universal, however. Only a third of heterosexual women said they were "highly feminine" as girls. A fourth of the heterosexual men, too, were nonconforming boys.

* But for homosexual men, gender nonconformity -- feelings of not belonging, of apathy or dislike toward what traditionally has been viewed as boys' play and a liking for traditional girls' play -- was the No. 1 predictor of their later sexual orientation. And "tomboyism" or something close to it was the second leading predictor for homosexual women. Homosexual involvement in adolescence was the leader.

* The signs, Bell said, show up "as early as 4 or 5 years of age." But homosexual development is often slow. Young homosexuals usually don't have fewer dates with the opposite sex. They just find they enjoy them less.

* Effeminate men and masculine women are most conspicuous among homosexuals, and they are the most likely to be the product of biological rather than social influence, but there is no single homosexual archetype. For instance, while 44 percent of homosexual men in the Kinsey group's sample were effeminate in manner, "macho" men can be homosexual as well. Nor was gentleness or effeminacy in manner necessarily an indication of homosexuality in men. Neither does the stereotype of a hard, dominating woman necessarily reflect homosexuality in women.

Masters has estimated that there are as many as 21 million homosexuals in the U.S. population, and that one man in three and one women in five has at some time had homosexual experience.