A federal commission advising the Food and Drug Administration has recommended approval of hyperthermia machines that use microwaves to treat cancer.

If, as expected, the FDA grants final approval this summer, hyperthermia would become a fourth treatment for cancer, with surgery, radiation and chemotherapy.

An FDA panel on radiological devices Thursday recommended giving BSD Medical Corp. of Salt Lake City approval to market a hyperthermia, or heat-making, machine to shrink some uncurable cancers in an effort to extend the life of seriously advanced patients.

"This is a palliative use. It will not cure cancers. I want to emphasize that," an FDA official said yesterday.

But he and some doctors predicted that before another year is out the FDA will approve use of hyperthermia in conjunction with radiation to treat a variety of earlier, still curable cancers.

Hyperthermia machines use beams of microwaves--the same kind that heat up kitchen microwave ovens--to heat cancer cells to 108 to 113 degrees Fahrenheit.

This is not enough heat to burn away cells. But it is enough, many scientists believe, to injure cancer cell membranes and upset the chemical pathways by which these cells reproduce to cause a cancer's otherwise inexorable spread.

The machine approved by the FDA advisory committee is, with full equipment, a $200,000 device. About 100 hyperthermia units are in use in research hospitals, including Memorial Sloan-Kettering Cancer Center in New York City and the University of Maryland Hospital in Baltimore, as well as in Indiana, Kansas, North Carolina, Utah, Vanderbilt and other university medical centers.

Reports so far have shown that hyperthermia is most effective on cancers no more than two inches beneath the surface, or on skin growths. Many tumors are only that deep, and breast cancer often recurs on the surface.

Many researchers also are burying needle-like probes within brain tumors to get maximum heat to the target area.

Dr. Jae Ho Kim of Cornell Medical College in New York last year treated more than 100 lesions in 38 patients. He reported achieving significant regression of tumors in 75 percent of the lesions treated with radiation plus hyperthermia, compared with 46 percent with radiation alone.

Dr. Richard Chamberlin of the National Cancer Institute said that the method is still being investigated. "But it does show great promise," he said. "It has a reasonable chance of carving out a niche for itself."

"Hyperthermia is definitely going somewhere," Dr. Gilbert Nussbaum of Washington University in St. Louis told the Washington University Magazine. ". . . I can remember one patient who had a tumor as big as an orange on the side of his neck . . . . We could see improvement with each treatment . . . .

"We have advanced now to the point that combined thermo therapy and radiation therapy can be used with optimism in breast cancer, cancer of the head and neck and skin cancer," Nussbaum continued. "In some cases it can be used in tumors that have spread to the lymph nodes."

Egyptian physicians 5,000 years ago poked heated sticks into tumors in an attempt to melt them.

Over the ages a startled doctor occasionally noted that a cancer had mysteriously disappeared after a patient had a high fever.

Now, said Dr. Bahman Emami at Washington University, " Our results are being repeated regularly here and at other research units . . . . That's why I say the field is exploding."