BALTIMORE, AUG. 5 -- Two groups of researchers today announced the first effective treatment for the most severe form of muscular dystrophy, a development that in many cases could delay for years the muscle deterioration that leaves victims of the disease unable to walk.

"This is the first medical agent that has ever shown success in treating this tragic disease," said Dr. Daniel B. Drachman, professor of neurology at the Johns Hopkins School of Medicine, speaking at a briefing here this afternoon. "But I do not want to imply that this is a cure. It is also not a treatment that we can recommend for everyone. But it is the first real ray of hope for those who suffer."

Drachman and his colleagues at Hopkins used the steroid prednisone over a period of years to slow the progress of the disease in a group of 16 patients with Duchenne's muscular dystrophy. Those treated with the drug remained able to walk for two to three years longer than the 38 patients in the study who did not receive prednisone. Another study released today by a team from the Washington University School of Medicine reported similar results with 33 boys who received the drug.

Duchenne's muscular dystrophy, the most common as well as the most severe form of the disease, is hereditary and afflicts an estimated one in 3,300 babies, almost always boys.

The disease is marked by a gradual, steady deterioration of the muscles, leading invariably to reliance upon a wheelchair and breathing difficulties as the muscles that control the lungs begin to fail. Few victims live beyond their 20s.

Prednisone is a powerful steroid. Its use caused serious side effects in many of the patients, including significant weight gain -- which can be particularly troublesome for people weakened by muscular dystrophy.

Other side effects included high blood pressure, cataracts and diabetes. Drachman cautioned parents of children with muscular dystrophy not to assume such treatment is in the best interest of their children.

"It takes a deeply committed family to make this worthwhile," he said.

But members of one family who had received the steroid treatment for years said today they would gladly do it over if given the chance.

"It kept me out of the chair until I was much more able to handle it emotionally," said Thomas Bailey, 19, who along with his 21 year-old brother, Stephen, took the pills for years under the supervision of doctors at Johns Hopkins. "I did things that I just could not have done without the drugs."

The median age at which children on prednisone became confined to a wheelchair was 13 for patients in the Hopkins study. For those who did not take the drug, the median age was 10.

Drachman said a large controlled study will attempt to confirm the findings at four medical centers. He also said that researchers will seek to isolate the actions of prednisone that cause the benefits in hope that better treatment will soon be developed.

Muscular dystrophy begins with tiny leaks in the membrane of the muscle cells that are apparent only under the most powerful microscopes. Calcium then enters the cells. Researchers think that the calcium may activate enzymes that then destroy the muscle.

Steroids may prevent that process, although scientists are not certain.

Last year scientists located the gene that causes Duchenne's muscular dystrophy. And medical experts hold out the hope that further research into its chemical processes will lead to treatment and a cure.