Doctors at the National Institutes of Health in Bethesda treated teen-ager Joe Kreuter's cancer for three years before they reached a painful decision. They kicked him out.

"We'd never encountered anyone like this," says Dr. Philip Pizzo, a pediatric cancer specialist who treated Kreuter for 2 1/2 years until the youth's dismissal last January. "We were really torn because Joe could be a very likable and charming kid. There were people here who cared for him very deeply."

What NIH doctors did not care for was Kreuter's practice of smoking marijuana in the hospital wards, although they tolerated it for many months while trying to persuade him to stop. They say he also passed out illegal drugs to other patients and once physically attacked a doctor.

Finally, even though Kreuter's rare form of cancer was unresponsive to treatment and doctors now believe his case is terminal, the 18-year-old Arlington youth has been barred from further treatment at NIH.

"What Joe presented was a very profound moral dilemma. What do you do when a patient -- especially when that patient isn't an adult -- tells us he doesn't want therapy?" asks Pizzo. "We tried to say, 'Look, Joe, we want to treat you but you're going to have to promise that you're going to leave drugs outside.' It just didn't work."

The decision marked the start of a nightmarish odyssey for Kreuter, who is able to cope with the pain of his illness only by taking morphine every four hours.

Too angry and disruptive to stay with his parents, he has spent much of the last year alone, living in vacant lots, sleeping on the streets and injecting himself with large doses of a powerful narcotic painkiller so it would not be stolen from him. He is now recovering from the latest of six operations at Arlington Hospital and faces life alone on $320 a month in disability checks and food stamp payments.

"NIH said I was trouble on the wards, but all I did was to tell the other patients that they would screw you over if you didn't watch yourself," says Kreuter, whose chest bears the scars of repeated surgery to remove tumors. On his back is an oval patch the size of a dinner plate where doctors grafted skin from his abdomen to cover burns from radiation therapy. His 6-foot-1 frame has shrunk to 110 pounds.

Medical experts say that Kreuter's case is an extreme example of the problems of treating the estimated 7,000 Americans below the age of 15 who develop cancer each year.

"What often happens is that adolescents fall between the cracks of the medical system," says Dr. Lucius Sinks, a Georgetown University cancer specialist. "If they fall under an adult care facility they're treated as adults even though they're not. If they fall under a child-oriented facility they get care oriented toward small children and they resent that. . . . There's this tremendous hostility and belligerence because they don't understand what's happening to them.

"These days, kids with cancer are living longer, but it's at the price of aggressive therapy that is often terribly mutilating and occurs at a time when kids are most concerned about how they look."

Kreuter, who suffers from undifferentiated sarcoma, cancer of the connective tissue system, admits he smoked marijuana, a practice he said NIH officials at first condoned. He denies attacking anyone.

"I was only a kid and my life was so good when this happened," he says, angrily pressing his nail-bitten fingertips against his eyelids to stop the tears. "I played basketball and I thought of going to college and now I just hurt. I don't really want to stay in the hospital but I have nowhere else to go."

In 1977, when Kreuter, the fifth of six children of an Arlington firefighter, was diagnosed as having cancer, his family and doctors were optimistic that chemotherapy and radiation and later surgery might help.

"All the time they were giving him these awful bunches of [painkilling] drugs and they said, 'Don't worry, we have ways of getting him off it'," recalls Eloise Kreuter, Joe's mother, a large curly-haired woman who shares a neat South Arlington apartment with her husband and youngest daughter.

Doctors at NIH say they were aware that the youth had become addicted to morphine and other narcotics that were prescribed to kill the frequently agonizing pain.

"We take the philosophy that pain medication is part and parcel of the treatment of cancer," says Pizzo, adding that Kreuter had experimented with marijuana before being hospitalized. "We knew that Joe had become addicted to narcotics so he was put on methadone. We were concerned about his drug dependence, but we have ways of controlling that. [the real] drug problem in the hospital was his use of marijuana [laced with] PCP. He passed marijuana out to the other patients."

Dr. David Pickar, an NIH psychiatrist who treated Kreuter, agrees. "He claimed the marijuana helped his nausea and it may have, but this is a government hospital and he was repeatedly told that this was against the rules. I'm not sure what one does with an adolescent who acts out and who can't be contained to fit in a very aggressive medical regime. You can say someone is rebelling against authority, but the ultimate authority is that you're going to die."

Many cancer patients undergoing chemotherapy have been given marijuana or its active chemical ingredient to control nausea and vomiting as part of research studies. The federal government and 24 states have controversial marijuana programs for such patients.

Before they discharged Kreuter, NIH officials made arrangements for him to be treated at the in-patient psychiatric facility at George Washington University Hospital. Less than three weeks after his admission there, Kreuter signed himself out because "they weren't helping me."

His parents say that as their son's illness progressed, they became increasingly unable to deal with him. "There's no question that the family was trying to do the best they could, but they had a lot of problems which (preceded) Joe's illness," says Pizzo. "Cancer can tear even the most stable of families apart."

Eloise Kreuter says her youngest son lived with the family briefly after he left GW Hospital. "He stayed with us for a while, but he became noisy and violent and the neighbors called the police so our landlady said he couldn't live with us." She says she searched in vain for a halfway house or group home for her son after relatives refused to take him. "Once the police brought him home when they found him sleeping in a field."

After that, Kreuter says he spent seven months drifting around Northern Virginia, sleeping on the streets, in abandoned buildings and staying for a few nights with friends and relatives. He says he regularly got prescriptions for Dilaudid -- a strong narcotic painkiller -- from two Arlington physicians who were treating him for cancer.

"I was getting beaten up and held up with a gun because I had all this medicine so I began to shoot it up," says Kreuter. "People would push you around, make you empty your pockets, stuff like that."

Six weeks ago he returned to Arlington Hospital for an operation on his lung. He is scheduled to be discharged soon and says that hospital officials are searching for an apartment. "I think an apartment will be okay," says the youth, who spends much of his free time researching cancer treatments. "What I'd like most is to get out of the hospital and live with my parents but I guess I can't do that."

That fact upsets Eloise Kreuter. "Joe and I have had problems in the past but that happens with lots of kids. I'm afraid he thinks his mother and father don't want him, but we do. We just kon't know what to do about all this."