Every week for three months last winter Tim J. Allen, a Baltimore car mechanic, went to Johns Hopkins Hospital for injections to curb what he calls his "sex addiction."

Convicted of molesting a 6-year-old girl, Allen was placed on probation for five years on condition that he participate in a Johns Hopkins program that uses Depo-Provera, a controversial drug designed to change hormonal balance and lower sex drive. With the help of the drug and psychiatric counseling, he says he is now able to contain his problem.

"It allowed me to control my urges," Allen, 32, said of the drug. "It was better than jail."

Allen is one of about 150 sex offenders who have been treated at a special "psycho-hormonal" clinic at Hopkins in the last two years, most of them as a condition of probation. The clinic's help, and use of Depo-Provera, also has been extended to seven mentally retarded youths at the hospital and to 12 inmates at the Maryland State Penitentiary.

Dr. Fred Berlin, a psychiatrist who directs the program, sees it as a pioneering effort to help men who usually are jailed rather than treated. "It's not so simple and naive as just getting a shot," he said. "We just suppress the urges so that people have an increased ability to control themselves."

Not everyone shares Berlin's enthusiasm. To some medical and legal experts, the program raises several troubling questions ranging from the conditions under which patients participate in the program to whether the drug should be given at all.

Depo-Provera, used by millions of women in Europe and elsewhere as an injectable contraceptive, was not approved in the United States for that purpose after tests showed it caused cancer in monkeys and beagles. The drug is officially approved only for treatment of cancer of the kidney and uterus, but under FDA guidelines, doctors in this country are free to use a drug, once approved for any purpose, as they choose.

"It makes a mockery of the whole concept of informed consent when your option is to go to jail or get injected with a carcinogen that can increase the risk of heart attack, " said Dr. Sidney Wolfe, director of the Health Research Group, which has fought approval of the drug. "It's human experimentation."

Dan Manville, an attorney with the National Prison Project of the American Civil Liberties Union, said he is concerned that prisoners might volunteer with the hope of impressing the parole board. "It's an indirect form of coercion," he said.

Berlin emphasizes that he has no connection with the parole process and that no one is forced to take the drug.

Authorities have struggled for years with various methods to treat sex offenders, including surgery to remove the testicles and parts of the brain. To many participants in the Hopkins program, Depo-Provera is viewed with relief resembling religious fervor.

"I'd crawl to Baltimore to get Depo-Provera if I had to," said a 57-year-old Philadelphia father of three. He credits the drug with freeing him from "a lifetime of misery" as an exhibitionist.

Currently, 90 men from seven states are receiving treatment at Hopkins. Most are receiving or have received Depo-Provera. About 70 men are there under court order, many because their attorneys learned about the program and presented it to the judge as an alternative to jail. The rest sought out the program.

Only a few of the men in the program have dropped out or been sent back to the courts because they posed a risk, Berlin said. These encouraging results are skewed, he acknowledged, because the program does not accept violent rapists, for example, or men who have not expressed a motivation to change.

The project had its origins in research with Depo-Provera performed 15 years ago by Berlin's predecessor, Dr. John Money, a psychiatrist who is credited with pioneering work in the treatment of sex offenders.

Money found that a high percentage of patients relapsed shortly after the drug was withdrawn. "In general, we believe many people will need to take it as a diabetic does insulin : indefinitely," Berlin said.

Berlin began experiments similar to Money's three years ago under the direction of the hospital's Joint Committee on Clinical Investigations. For the last 18 months, both Berlin and the committee have considered the program "treatment" rather than an experiment, and patients or their insurance companies are charged for the treatment.

The mentally retarded males are receiving the drug to control sexual activity such as masturbating in public. Berlin said the drug has been explained as much as possible to the youths, and their guardians had given their consent.

About 20 inmates participate in the program, with 12 receiving Depo-Provera. "Some people say there's no need in prison to take the medicine," Berlin said. "But many men are unable to control their thoughts and unable to control their urges. They desire to have peace of mind."

Dr. Wayne Barry, a Baltimore physician who was medical director for the penitentiary for the last five years under a contract arrangement, said neither he nor anyone at the prison monitored the project. "I thought it might add something," Dr. Barry said. "Whether it did or does, I don't know. I'm pretty confident it didn't hurt anyone."

Patients at a recent counseling session said they had been informed of the risks and side effects, which include weight gain, increased blood pressure and menopause-like symptoms. "It's not feminizing," Berlin said. "They don't grow breasts or stop shaving." But the drug does lower the level of male hormone, testosterone, in the blood, and one participant who wished to father a child stopped taking the drug with Berlin's approval.

Although Berlin and his two associates send occasional reports to the Upjohn Co. of Kalamazoo, Mich., the drug's manufacturer, they are not working on a formal study, he said. The company provides the drug for the program at no charge and has a government drug application for its use on males, according to Upjohn spokesman Joe Heywood.

Because the hospital no longer considers the treatment an experiment, records spelling out the success rate are not kept, Berlin said. The clinic has plans to begin a study with a control group in order to test the drug's efficacy.

"For the majority of these people, we're not doing it under the IND the formal government process of approving new uses for drugs because we don't think it's experimental," Berlin said.

Operating the program outside of a controlled experiment angers Wolfe of the Health Research Group. "This sounds like 35 years ago when doctors used DES on pregnant women without good controls," he said.

The federal Food and Drug Administration has not yet ruled whether the drug causes cancer. That decision may come next month when a special appeal board on the ban reviews tissue slides on monkeys that received the drug, according to FDA spokesman Ed Nida.

But the men who have relocated to Baltimore or drive here each week to take the drug said the possibility of a medical danger seemed remote in comparison with the danger of continuing destructive actions that harmed others.

"I jumped at the chance to take it," said one 35-year-old Washingtonian, who was recently married after years of finding only young males sexually attractive.

"I thought it was hopeless. It hasn't been easy. But I can definitely say the drug helped. It made me calmer. I didn't have the overwhelming desire."

He continues to attend weekly counseling sessions, one year after his probation ended, because "I just want to be reminded."

A 32-year-old man from Toledo, who has been peeping in windows since childhood and is facing first-degree rape charges, said his three weeks on the drug "has got me away from something I've been carrying around for 24 years."

His company at a recent counseling session at the hospital consisted of 20 other men, ages 17 to 57, who are admitted child molesters, rapists, voyeurs, exhibitionists and sadists. The group included a former Washington lawyer, an ex-college basketball star from New Jersey, a Baltimore plumber and a former firefighter from Anne Arundel County.

An essential part of the program is the intense counseling its participants receive from Berlin and other staff members. Berlin, a tireless worker, emphasizes to his patients the emotional and physical harm they have caused to their victims, and the necessity of change.

In addition to group sessions, Berlin and his assistants meet with the patients individually and help them seek jobs and housing.

"I could never prove to the cynic that these men aren't all just con artists using this to stay out of jail," Berlin said. "But we know the lives we've stabilized and the people we've helped more than jail."

Only offenders eager to help themselves are admitted to the program, Berlin said. All are hospitalized for three to four weeks of tests and counseling and, for those whose problems might be helped by Depo-Provera, trial doses of the drug. Shots then are administered once a week, before or after group counseling sessions.

"If men are lying to me, skipping appointments or refuse to take the medicine," they are dropped from the program, Berlin said.

The Baltimore program has sparked interest in several states, including New Hampshire and Illinois. Last week the Oregon legislature approved legislation that urges that medications such as Depo-Provera be included in treatment programs for sex offenders.

Although no drug is specifically mentioned, the bill's sponsor held a hearing to acquaint legislators with cases where Depo-Provera had been successful.

Berlin said he is concerned that other states not rush to Depo-Provera as a cure. "It takes years of counseling to control behavior," he said. "The drug only takes the edge off."