The recent request by a Texas man to be surgically castrated instead of standing trial for the rape of a 13-year-old girl has revived one of the most emotional questions in medicine and law: what works in treating sex offenders?

Therapists who treat rapists and child molesters often passionately disagree about whether drugs, behavior modification or re-education is most effective. But they are united in the view that castration is useless and probably counterproductive in preventing future sexual assaults.

"There's a high degree of folklore about what castration does and doesn't do," said John Money, emeritus professor of medical psychology and pediatrics at Johns Hopkins School of Medicine.

The belief in the efficacy of castration, said Money, who pioneered the treatment of sex offenders, "is based on a popularized belief from childhood" -- that castrated animals are asexual. "But as anyone who grew up on a farm can tell you, there's a gigantic difference if you {castrate} animals when they are newborns or after puberty when they have gained sexual experience" and can continue to have sex.

The most common misconception about castration is that it involves amputating the penis. In fact, surgical castration usually involves removal of the testicles that produce the male hormone testosterone. The penis is left intact.

Men who are castrated often are still able to have an erection and may be capable of intercourse. Their sex drive is diminished because the testicles are no longer present to produce testosterone. But the drive is not eliminated. A small amount of testosterone is also produced in the adrenal glands; if the supply from the testicles is reduced, the adrenal glands compensate and produce more of the hormone.

Last week, relatives of the Texas defendant said he had changed his mind about being castrated. Yesterday, the judge withdrew his approval of the procedure, saying he was unable to find a doctor to perform it. Publicity about the case, however, has rekindled public debate about castration.

Rape crisis workers say that violence, not sex, is the real problem, which castration fails to address. "This misfocuses the issue and feeds into the myths about rape," said Denise Snyder, executive director of the D.C. Rape Crisis Center. "Sexual assault is a crime of violence and aggression . . . not the product of an uncontrollable sex drive."

The problem is often in the brain, not the testicles, said Barbara K. Schwartz, director of the Sex Offender Treatment Program at Twin Rivers Correctional Center in Monroe, Wash. A rapist who has been castrated "could still be a phenomenal danger. He can go out and, instead of raping people, he can assault them with broom handles or bottles or beat them up or kill them."

Castration is one of the oldest and most controversial methods of treating sex offenders. It has been used infrequently in the United States in the past 100 years, although in some states, among them Oklahoma and California, sex offenders have been castrated. The practice has been more widely used in Germany and Scandinavia.

In Denmark in the late 1950s and early 1960s sex offenders were permitted to choose prison or surgical castration. Research on 900 castrated sex offenders showed that the rate of repeat offenses was low, about 5 percent. But 46 percent of the men said they continued to have intercourse.

Most European countries have abandoned surgical castration in favor of so-called chemical castration: weekly injections with drugs called anti-androgens that blunt the sex drive. The best known of these drugs is Depo Provera, a female sex hormone first used in the U.S. by Money at Hopkins in 1966.

Most experts say that Depo Provera works best if it is administered in conjunction with other forms of therapy. In most cases it is prescribed only for men whose compulsive behavior or fantasies are so overwhelming that they are unable to participate in other forms of treatment.

Depo Provera, however, can have side effects, among them weight gain, hot flashes and hypertension. As a result, many men stop taking it, according to Judith Becker, professor of psychiatry and psychology at the University of Arizona College of Medicine. And while Depo Provera blunts the sex drive, it does not redirect it. That is the aim of various forms of therapy used in the approximately 1,500 prison and community-based programs that treat rapists, child molesters or pedophiles, and men who commit incest. Becker, who has treated hundreds of sex offenders, says that studies have shown that about 40 percent of rapists will repeat their crimes So will pedophiles who are interested exclusively in young boys.

Treatment varies according to the offender's problem, but the goal is the same: to prevent another sex crime. In the case of pedophiles or men who suffer from paraphilias -- intense, compulsive fantasies about deviant sex acts -- treatment initially focuses on robbing fantasies of their power by associating them with electric shock or an unpleasant smell, a behavior modification technique known as aversive conditioning.

In the case of a child molester attracted to 10-year-old girls, severing the connection between arousal and children might mean fantasizing about a little girl and then sniffing an ammonia capsule.

This technique would typically be repeated 20 times a day for eight to 10 weeks. "It produces a mild phobic response," said Steven H. Jensen, a Portland, Ore., therapist who is past president of the Association for the Behavioral Treatment of Sex Offenders.

The goal of aversive conditioning, according to Anthony Eccles, a Canadian psychologist with long experience treating sex offenders, is for the patient to substitute an "appropriate fantasy with a consenting adult" for a deviant fantasy involving a child. Some programs also teach participants to recognize the people or situations likely to trigger a relapse, a technique also used in drug and alcohol treatment. Just as recovering alcoholics avoid bars, rapists might be taught to stay away from violent movies and child molesters would learn to eschew school playgrounds or parks.

Many programs also attempt to change a sex offender's thoughts through intensive re-education, a process Jensen likens to brainwashing. "If you put in an accurate message often enough, you can change those cognitions," he said.

In order to do that, therapists first must overcome the disordered thinking common among sex offenders. Many deny or minimize the impact of their behavior. "You can't rape women and abuse kids unless you can twist the world in quite remarkable ways," said Eccles, clinical director of the Kingston Sexual Behavior Clinic in Kingston, Ontario. Often, he said, men who commit incest attempt to justify it by insisting that "sex with their 13-year-old stepdaughter was somehow educational."

Some programs teach social or sexual skills, which are important in overcoming feelings of inadequacy and powerlessness, according to Jensen. "We get people who've never had a date, people who are sexually ignorant," said Jensen. The private treatment program he runs in Portland offers skills training that "can mean anything from kissing techniques to how to have intercourse to how to maintain a relationship." Some programs offer couples or family therapy, particularly in incest cases.

There is a consensus among experts that long-term individual psychotherapy, the primary method of treating sex offenders a generation ago, doesn't work and many be harmful. "These guys are masters at co-opting therapists," said Schwartz. Too often, individual psychotherapy "recreates the kick" by encouraging them to recount their crimes in graphic detail, she added.

Although each method has its ardent proponents, the effectiveness of sex offender treatment programs is far from clear. Because the field is new, there are few controlled scientific studies evaluating different regimens. Furthermore, the skill and training of therapists varies widely and many programs use an eclectic mix of therapies that makes comparison difficult.

"People really don't know what works," said Fay Honey Knopp, director of the Safer Society Program, a national referral center for treatment of sex offenders based in Vermont.

Some programs claim to have extraordinarily low recidivism rates, statistics Jensen and others say may be misleading. Sex crimes are notoriously underreported, and most programs track participants only for a short time after leaving treatment when the risk of relapse is lowest.

"Recidivism rates are only based on what you know," such as the number of re-arrests, Jensen said. "The problem is what you don't know."