A new treatment for brain tumors that has achieved remarkable success was announced Friday by Georgetown University researchers.

The researchers gave a chemotherapy drug, cis-platinum, to 10 children whose tumors had continued to grow despite treatment with surgery, radiation, and other kinds of chemotherapy. Three of the children, who otherwise would have been expected to die within months, are well more than two years after first receiving the drug. Three others had temporary but dramatic improvement.

Cancer experts at other medical centers are elated by the findings because, although preliminary, they provide real hope of progress against malignant brain tumors, a cancer that has been discouragingly unresponsive to surgery, radiation and other drugs.

"Their results . . . are quite exciting," said Dr. Gary Witman, a senior clinical investigator at the National Cancer Institute's division of cancer treatment. "It may well be that platinum is the best drug available for brain tumors."

Although cis-platinum has been used with some success against other kinds of cancer since the early 1970s, Witman said many experts shied away from trying it for brain tumors because they believed it would not penetrate to the cancers. But they have been proved wrong.

Except for leukemias, tumors of the brain and nervous system are the commonest kind of cancer in children under age 15.

Dr. Lucius F. Sinks, who directed the research, said he has been looking for 20 years for a drug that would prolong the survival of victims after the tumors have been removed surgically.

Of the 10 patients Sinks and his coworkers have treated with cis-platinum so far, three have responded extraordinarily well to the treatment.

"The disease is static and they show neurologic improvement," he said. In two of them the tumors seem to be completely gone. "You have to come to the conclusion that the biology of the tumors is changed by this therapy," he said.

The childrens' recovery is the more remarkable because all three were desperately ill when they first received the drug. One 7-year-old boy had been in a coma for four weeks when he was given cis-platinum. Two weeks later he left the hospital, and now, except for some defect in his memory, he is normal.

Another, 19-year-old John Daley Jr. of Bethesda, was confined to a wheelchair with a tumor that had recurred after maximum doses of radiation. "It was put to us . . . that this (cis-platinum) was one of the only alternatives modern medicine had to offer," his father, John Daley, said.

Now, Daley said, his son is walking without a cane and has just started college.

The third patient, according to Sinks, also continues to improve, although he is handicapped by damage that the tumor did to his brain.

Three other patients had dramatic responses to cis-platinum, but two had to go off the drug because of side effect, and later died. Another child apparently recovered from his tumor after receiving cis-platinum, but died of an infection that may have been a complication of other medicines he was receiving.

Like other chemotherapy drugs, cis-platinum works by deranging vital chemical constituents of tumor cells, and it can damage normal cells as well. The drug forms cross-links between strands of DNA, the master molecules in the nucleus of all cells that program the synthesis of proteins that the cell makes in order to grow and reproduce.

Patients receiving cis-platinum suffer nausea and vomiting and often develop ringing in the ears and some hearing loss. But the drug's more serious side effects, which can limit the dose an individual patient can be given, are damage to the kidneys and nerves. Two of the 10 patients treated by the researchers apparently died of kidney damage caused by the drug.

Because this was the first time cis-platinum had been tried, Sinks said the group chose patients with a variety of kinds of brain tumors that had denied all other forms of treatment. The next step, he said, will be to use cis-platinum right after surgery as the first form of chemotherapy given to brain tumor patients.

Witman said the Georgetown group's results have encouraged researchers at Yale University and the Mayo Clinic to try cis-platinum to treat brain tumors in adults -- particularly an extremely malignant form of cancer called glioblastoma multiforme, which most often strikes men in the prime of life. No results are available yet.

He added that the drug seems to sensitize tumors to the effect of radiation, so that in addition to its own action, it may enhance the success of radiation therapy.

With the introduction of the platinum compounds we have a promising new lead in prolonging survival" for children and adults with brain tumors, he said.