As the number of child sexual abuse cases rises locally and nationally, a new, more complex picture is emerging of the individual who does the unthinkable with innocent young victims.

A school psychologist, a former scoutmaster, a wrestling coach, a former gym teacher and a school aide are among those who have been arrested in the Washington area in recent months on charges of sexually abusing children. There's also been "a steady, steady increase in the number of victims coming to our attention," reports Joyce Thomas, director of the Child Sexual Abuse Program at Children's Hospital National Medical Center.

Since the Children's Hospital program began about seven years ago, the number of children and adolescents treated for sexual abuse has risen from 200 to more than 800 cases a year. Already this year, there's been a 25 percent increase in the number of victims over those treated last year, and Thomas says that "this past month we've seen a dramatic increase in the number of children with sexually transmitted diseases."

An estimated 200,000 to 600,000 children and adolescents are sexually abused each year, a 200 percent increase over 1976, according to the National Committee for Prevention of Child Abuse.

Whether this trend reflects a growing number of cases or merely better reporting of sexual abuse victims is not known. But one thing is certain, experts say: child sexual abuse cuts across all races, religions and socioeconomic classes.

"We're dispelling the notion of a certain type of profile [of child sex offenders]," says clinical psychologist Nicholas Groth, codirector of the Sex Offender Program at the Connecticut State Correctional Institute. "What we're talking about is a behavior problem that can cut across all sorts of conventional psychiatric problems.

"It's like talking about alcohol abuse. There's not a certain type of person who is an alcoholic. There are college graduates that are alcoholics and high school dropouts that are alcoholics." The same goes, he says, for child sex offenders.

The majority of child sex offenders -- perhaps as many as eight out of 10 -- don't use force when they approach a child, Groth says. Instead, they typically befriend them.

Offenders often gain access to the child, Groth notes, "through enticement," or by "persuading the child to cooperate" -- which typically leads to great emotional conflict for the youngsters and decreases the likelihood that an offense will be reported.

Other findings suggest:

*There may be a great overlap between the various types of sexual offenders. Where the flasher and the peeping Tom were once thought to limit their deviant behavior to those activities, now there's evidence, says psychologist James Garbarino, director of the Erickson Institute in Chicago, that "the majority of sex offenders engage in multiple deviation."

*A majority of sex offenders begin molesting children in adolescence. One new study by researchers Judith Becker and Dr. Gene Abel from the New York State Psychiatric Institute suggests that by age 19, more than half of child sexual offenders -- some 65 percent -- already have committed at least one offense.

*Those who engage in incestuous sexual activity with children are likely to make advances to children outside the family as well. "Those who offend within the family," Garbarino reports, "often have also offended outside the family."

Sexual abuse of children continues to be committed predominantly by men. "That seems to be true in a variety of cultures," says Dr. Fred Berlin, director of the Sexual Disorders Clinic at Johns Hopkins University Hospital in Baltimore. "Yet having said that, there is a percentage of women who are also involved in sexual abuse of children," but the actual numbers are unknown.

Incidents in which females sexually abuse children often go unreported, experts say.

As evidence, Connecticut's Groth points to some 2,000 sexual offenders that he's treated at the state prison in Somers during the past 20 years. All but four of those prisoners were men, and more than 90 percent had been sexually abused as children. A quarter of these men had been sexually abused by women -- an older sister, step-mother, neighbor, teacher.

Being sexually abused as children is one characteristic that many convicted sex offenders share. But experts say only a very small percentage -- perhaps just 1 to 2 percent -- of children who are sexually abused grow up to become abusers of other children. "It's a lot more complicated than we understand," Groth says.

Exactly what motivates these offenders is still a mystery. "Many start out looking for affection and companionship with children," Berlin says, "and then become interested in sex."

Sexual offenders often look for "kids who have these same needs for affection and companionship and may not be getting that at home," Berlin says. "The kids who are most vulnerable are craving affection."

Sex offenders also target children who are interested in learning about sex, but whose parents won't talk with them about it, Groth says. Convicted sex offenders have told him that "one of the lures we have is that kids are curious about sex, and they can't go to their folks with questions."

Another sex offender told Groth that he's "never been successful in seducing a boy who had a good sex education and a good relationship with his father.

"In one sense, the sex offender can capitalize on what we as parents don't provide to our kids . . . I tell parents to tell their kids not to trust adults who would encourage them to do something that their parents would forbid or that the law says is a crime."

Another approach sex offenders use is entrapping children through experimentation with drugs or alcohol, which is then used to blackmail youngsters into engaging in sexual activity. The child thinks, Groth says, " 'How can I tell anyone what happened?' "

To help prevent sexual abuse against children, experts advise good sex education, begun at an early age, which teaches children what is appropriate behavior and what's not.

"And the child and the parent must know each other better so the child doesn't feel hesitant about talking" if something does happen, says Dr. Mary Calderone, adjunct professor in the Program on Human Sexuality at New York University and cofounder of the Sexual Information and Education Council of the United States.

The key to combating the problem, says Children's Hospital's Thomas, is preventing child sexual abuse in the first place. That means a greater focus on the offender -- identifying, rehabilitating and preventing future abuses. Often, this is not very popular with the public. "People get the mistaken idea that there are two sides -- either you're for the offender or you're for the victim," says Dr. Fred Berlin, director of Johns Hopkins Sexual Disorders Clinic.

The real focus, Berlin says, should be on "learning more about what motivates the people who sexually abuse to behave this way" in an effort to prevent future offenses.

Once an offender gets started, notes Erickson Institute's Garbarino, the "number of offenses per offender is staggering. The adolescent who is showing signs of sexual offense is the key place to intervene.

"This doesn't seem to be a problem that goes away. The kid who starts exposing himself to other kids just shouldn't be passed off."

As for treatment, Connecticut's Groth says: "None of us talk cure. We're talking about control of a problem, like an alcoholic learns to control an addiction problem."

One person who has learned to control his problem is Jeff Youens, a 39-year-old former school board member and the married father of two sons. Youens, who lives in Southwick, Mass., served 15 months in a Massachusetts County jail for engaging in sexual activities on separate ocassions with two 15-year-old boys -- one of whom he met at church.

In 1982, the case was splashed across the front pages of local newspapers near the small town -- population 10,000. Youens lost his job, but his wife and family stuck by him through the ordeal. Following jail, months of therapy and an interim job as a bell captain at a local hotel, Youens landed a new job with a travel agency, but only after making full disclosure of his past to his employer.

"You have to be willing to admit that there might be some kind of problem and then do something about it," Youens says.

"I knew there was a problem within myself, but it was much easier not to do anything about it. But in hindsight, even if I did want to do something about it, I wouldn't have known where to go."

Today, he and his wife lead weekly self-help groups for child sexual offenders and their spouses -- hoping, he says, to aid themselves and others in combating their disturbing problem.