New study on sexual abuse of children;The Best Kept Secret: Sexual Abuse of Children, by Florence Rush. Englewood Cliffs, N.J.: Prentice-Hall. $11.95.

Florence Rush's conclusion that the "sexual abuse of children is the most muted crime" is highly disturbing. And her statistics -- among them that 25 million young women in the United States will experience sex with a male adult before age 13 -- are, to say the least, alarming. What is also very disconcerting is that Rush, a veteran psychiatric social worker and women's-rights activist, offers precious few suggestions on what to do about this problem.

In recent years, the focus of professionals in the child welfare field has centered on child abuse in general. And a wide range of programs -- including "hot lines," in-school and in-home education, and news media public service shows -- have popped up to help potential abusers, victims, and their families alike. Fallout from many of the child-abuse studies of the 1970s indicates that sexual abuse is a prevalent part of this problem.

It hasn't been until recently, however, that researchers have begun to concentrate on this aspect. The taboo word is incestm .

A few movies, among them "luna" and "Chinatown," have made a pass at the subject. Television, with mixed success, has also taken a few stabs at it. But the print media have had difficulty presenting it. Earlier this year this reviewer attended a symposium sponsored by the highly respected Bush Institute for Child and Family Policy, during which editors from the major media discussed how their publications or stations tackled the subject. Responses ranged from "delicately" to "not at all."

The author is to be commended for coming at it head on, dramatically if not delicately. Her message is clear: Incest is a problem, perhaps growing to major proportions in the US because it is largely unreported and unchecked. The abuser is almost always an adult male (often a father or uncle), and the victim is a female child, sometimes five years old or younger. Because men are the perpetrators of this crime, they are not likely to be part of the solution, the author suggests.

Rush's hard line against men in general is perhaps the weakest link in her presentation. Only in her final chapter does she concede that "not all men are child molester . . . some love children," after searing reinforcement throughout the book of a blanket indictment of males in general.

Also questionable is the author's historical analogy in which she traces sexual abuse of children to ancient marital customs and even scores the Scriptures for not specifically forbidding father-daughter incest.

With due respect to the author for her diligent research, one might take exception to her conclusion that the problem is only a women'sm problem and can be solved by improving the social and economic plight of women. Obviously, fair-minded people applaud efforts to break down all discrimination, including that on the basis of sex. But it must be the responsibility of the whole of society to protect children, both male and female, from abuse and exploitation.

"The Best Kept Secret" is useful, though flawed, book about a subject we will be hearing a lot more about. Sometimes overly graphic in its descriptions, the book is obviously not for everybody.