Two University of Maryland researchers earlier this month tried a daring new treatment on a patient with a lethal brain tumor: they implanted an antenna in the man's brain and bombarded the cancer with microwaves.

The patient -- a 28-year-old European executive whose cancer had recurred after surgery, radiation and chemotherapy -- is up and around at the University of Maryland Hospital, with no apparent ill effects from the antenna or three brain-heating treatments.

"After months of worrying, it turned out to be remarkably easy," said Dr. Michael Salcman, the 34-year-old neurosurgeon who performed the operation.

The researchers' tests on animals had shown them that the waves can heat a portion of the brain to a temperature that kills tumor cells, but leaves normal cells unharmed. If this first patient's tumor shrinks during the next few months, it will mean microwaves are a powerful new tool for treating one of the worst forms of cancer known.

"It's a promising area," said Dr. Allen Lichter, head of the radiation therapy section at the National Cancer Institute. "There's no question that heat kills cells.Whether it's going to have the selective effect on tumor cells, more than normal tissue, remains to be seen."

Microwaves have been used experimentally on a few other kinds of cancer, but this is the first time they have been tried on the human brain or delivered through an antenna, according to George M. Samaras, an electrical engineer and neurophysiologist at the University of Maryland who developed the apparatus with Salcman.

The two men had been testing microwaves for about two years on animals' brains, and had waited months to find a suitable patient to try their idea. Both said they were worried that the heating might cause the brain to swell and raise the pressure inside the patients's skull dangerously high. But no complications occurred.

The patient, a wealthy European who asked the doctors to keep his identity confidential, had a brain tumor called glioblastoma multiforme, which is so lethal that Salcman said none of its victims live more than five years. He developed the tumor two years ago and it recurred recently in spite of surgery, radiation therapy and chemotherapy that he recieved in Europe.

Salcman operated on the man on June 12, and was able to remove about half the tumor, which he said was the size of a tangerine. To cut out the rest would have destroyed a vital part of the brain.

During the operation, Salcman implanted in the tumor a fine wire antenna designed by Samaras. The antenna contains a temperature-sensing device and a cable that can be hooked up to a microwave generator. Then, with Samaras at the controls, they delivered enough microwaves to heat the area of the tumor to 113 degrees Fahrenheit for 30 minutes -- 13.5 degrees above the normal brain temperature, 99.5.

Later the same day, they left the antenna in place, and heated the tumor again, this time for an hour. Two days later, on June 14, they performed a final hour-long treatment and removed the antenna.

Samaras said the man was fully awake for the final treatment, and felt no pain. "He was talking a blue streak the whole time," Samaras said. "We were just tickled to death. . . . There was just nothing [for the patient] to tolerate."

"He said heating to 45 degrees does not "cook" the brain, but produces "a local fever state." "Up to 41 degrees Centigrade (105.8 degrees Fahrenheit), all cells including tumor cells are happy," he said.

Salcman said that so far the patient's condition is about the same as he was before the treatment, and that it will be weeks to months before the researchers know whether they have succeeded in retarding the tumor.

Samaras said the main risk of microwave is damage to heat-sensitive organs -- cataract-formation in the lens of the eye, sterility from damage to the testes, deformities to the fetus from exposure during pregnancy -- but that these effects do not occur at the temperature used in his treatment.

He added that the antenna delivers waves to a portion of the brain only one to two inches across. The microwaves are the same as those generated by a microwave oven, but Samaras emphasized that the brain is not heated to nearly as high a temperature as food in an oven would be.

Like visible light, radio waves, and X-rays, microwaves are a form of electromagnetic radiation. They and other kinds of radiation are being tried in a number of cancer centers to produce hyperthermia -- heating of body tissues.

Samaras said hyperthermia has a long history. A papyrus dating from 3000 B.C. reports the use of a "fire drill," a hot stick that was pushed into tumors. Heat therapy was used by the ancient Greeks, and in 1866 a Dr. W. Busch reported the disappearance of a patient's malignant tumor after an infection that caused a high fever.

He and Salcman are now developing a device like a football helmet, which could deliver microwaves to a brain tumor without surgery. They see the antenna as only a temporary technique.