The largest and most extensive review of child sex abuse cases ever undertaken has revealed this surprising portrait of the typical offender: Almost always, the sex offender is a male. He typically begins molesting by age 15 but often starts even younger. He molests an average of 117 youngsters, most of whom do not report the offense. He engages in a variety of deviant behaviors that may include everything from window peeping to rape. His victim is likely to be a boy he knows.

These are conclusions reached by Dr. Gene Abel of Emory University in Atlanta, after studying 571 sex offenders who had committed 67,000 cases of child sex abuse. The study was funded by the National Institute of Mental Health and conducted with psychologist Judith Becker, director of the sexual behavior clinic at the New York State Psychiatric Institute and Clinic. Results will be published in an upcoming issue of the journal Archives of General Psychiatry and in the Journal of Interpersonal Violence.

"Everyone is so surprised that a priest is a child molester, or that a school teacher is a child molester," said Abel. "I am flabbergasted that anyone would be surprised. Child molesters select out jobs to access kids. That's why they become pediatricians, child psychiatrists and they work in boys camps in the summer."

Abel presented the findings of his 10 years of research at the annual meeting of the Academy of Behavioral Medicine Research, held here earlier this month.

A psychiatrist specializing in the treatment of sexual behavior, Abel says his work is different from most studies of sex offenders because other studies have usually focused on people in prison. While offenders in prison are often promised that their statements would not be used against them, Abel said that few jailed sex offenders are willing to speak freely about what other crimes they may have committed.

"I believe that most of the information that is in the scientific literature is irrelevant because of the confidentiality issue," he said. "Quite frankly, arrests for sex offenders have very little to do with what crimes they have committed."

As evidence, Abel pointed to the difference between what convicted child molesters said in a probation office and what they said in his clinic.

Sex offenders in probation offices were asked, "How many sex crimes have you committed?" The men usually reported committing one to four sex crimes -- figures that agreed with their arrest records.

Later, these same men were asked the same question at Abel's sexual behavior clinic. This time federal authorities guaranteed in writing that the researchers would never be required to testify in any U.S. court about the interviews, and the sex offenders were identified only by number, not by name. Under these conditions, they confessed to committing an average of 75 sex crimes each.

"There is a vast difference in the information one collects dependent upon the confidentiality," Abel said.

Abel's research has also dispelled several other myths about sex offenders.

Sex researchers and police have long believed that men who expose themselves or peep into windows are unlikely to rape a woman or attack a child. Other widely held opinions are that obscene phone callers rarely, if ever, carry out their lewd suggestions, and that the man who fondles a neighbor's child would never do the same with one of his own children.

What Abel finds, however, is that when sex offenders target their victims, they "cross gender, they cross age, they cross familial relationships.

"They are doing all sorts of things."

In his study, 208 men confessed to molesting young girls from outside their families. "Out of those," Abel said, "37 percent also had histories or were currently molesting boys outside the home, 30 percent were molesting girls inside the home, 10 percent were molesting boys in the home, 20 percent were rapists, 28 percent were exhibitionists, 14 percent were voyeurs, 10 percent were frotteurs they touched women in crowds , 4 percent were sadists and 20 percent were doing other things."

The study also revealed new information about exhibitionists. "Exhibitionists are just supposed to be nice friendly folk who just flash, right?" he said. "That's not the case."

Abel found that almost half the exhibitionists in his study were also molesting children. One in five of these men were victimizing children in their own homes. Slightly more than 20 percent were raping women, and close to 30 percent were peeping in windows.

"What does this tell us?" Abel asked. Sex offenders "do everything." Myth No. 2: Girls more often than boys are the victims of child sexual abuse.

Abel's study suggests that boys are far more likely to be victims of sex abuse than previously believed. It is estimated that two thirds of all victims molested outside the home are boys.

While girls are more frequently the victims of hands-off crimes, such as exhibitionism and The typical sex offender engages in a variety of deviant behaviors that may include everything from window peeping to rape. window peeping, Abel said, boys are more likely victims of hands-on attacks, which involve some form of physical sexual abuse.

Hands-off crimes occurred less frequently than hands-on and involved about 40 percent of the children in the study. Six in 10 of these youngsters were age 14 or older, and girls constituted "99 percent of all the hands-off behavior targets," Abel said. This is why he believes that girls are considered the most likely victims of sex abuse.

In hands-on crimes, the majority of victims studied -- some 62 percent -- were boys.

"The big sex crime of child molestation is against boys," Abel said. "And those who molest boys molest in big numbers."

For the 153 offenders studied who had sexually attacked young boys, the average number of molestations was 281. Those who molested girls had committed an average of 23 molestations. By comparison, 126 rapists studied had raped an average of seven times. Myth No. 3: Sex offenders of children don't begin their crimes until later in life.

"We asked all of these individuals how old they were when they started to do whatever they did," Abel said. Approximately half reported beginning to attack children or engage in window peeping or exhibitionism by age 15. Some said that their deviant behavior began as early as age 8.

"What does that mean?" Abel said. "These problems begin at a very early age." Yet most current efforts at curbing child sexual abuse focus on treating victims -- a method which is "irrelevant in terms of prevention," he said.

Other reasons Abel advocates early detection of child sex abusers are these statistics: Sex offenders 18 and younger reported an average of seven child or teen-age victims. Sex offenders older than 18 reported an average of 380 young victims.

"That's a 50-fold increase in the number of victims," Abel said. "That's another reason why we need to do something about sex offenders at an early age." Myth No. 4: No good treatment exists for sex offenders. They must be put in jail.

"The treatments are already available," Abel said. "They've been tested . They're rather inexpensive. We can treat 10 outpatients for every one incarcerated patient."

In a companion study, Abel and Becker found that behavior therapy, designed to change how sex offenders think and act, can be successful in treating men with these problems. "The success rate is running between 85 and 87 percent," Becker said. A new study of 110 teen-age offenders, 13 to 18 years old, being conducted at the New York State Psychiatric Institute, suggests that the behavior program can also help the very young offender, Becker said.

But the real difficulty, Abel said, is how to get the public to accept the fact that the majority of sex offenders do not go to jail. One out of 80 crimes actually leads to an arrest. Even those who are convicted spend an average of only three years in prison. "Then they are right back out on the street," Abel said.

"The people who molest your children are your neighbors," he said. "They didn't fly in from out of state." When sex offenders are caught, they are typically jailed, he said, because "quite frankly, everyone kind of wants an eye for an eye.

"But we have to stop getting so emotionally involved in the situation and get concerned about preventing these crimes by helping these individuals control their behavior."

The current system of treating children after they have been molested is "a meager attempt," he said that does nothing to prevent the attack from occuring in the first place.

"There will never be enough money, there will never be enough therapists to do that," he said. "It's not going to work."