About 400,000 men are treated each year for enlarged prostates, which makes urination difficult. Costs top $3 billion a year. The alternative therapy, first devised in Europe, uses a microwave device inserted into the urethra, the tube that conducts urine from the bladder to the exterior.

So far in the U.S., 150 men have been treated with microwave therapy, and symptoms have improved on average by 70 to 80 percent, about the same percentage as in Europe. Dr. Dennis Pessis, a urologist at Rush-Presbyterian-St. Luke's Medical Center in Chicago, said "the safety of this procedure has really been established. Now we're going to look at efficacy. The initial results are very promising."

The federal Food and Drug Administration has given the green light for 250 more American men to be treated. If tests go as hoped, microwave treatments could become generally available sometime in 1993. Dr. Kevin Tomera, a urologist at Mayo Clinic Jacksonville in Florida estimated that microwave treatment will cost $4,000 or so as an office procedure. Prostate surgery, which requires hospitalization, costs $10,000 to $12,000, Tomera said.