A "modern medical miracle" that uses shock waves to shatter concrete-hard kidney stones into sand-like particles without injuring surrounding tissues received government approval for commercial use yesterday.

It offers a revolutionary treatment approach that experts say could eliminate the need for 80,000 costly surgical operations each year in the United States and drastically reduce the time a patient is hospitalized and recuperating.

In announcing Food and Drug Administration approval for its marketing, Health and Human Services Secretary Margaret M. Heckler said the device with the tongue-twisting name "lithotripter" was "an authentic modern miracle," not only because of its medical importance but because it will help reduce health care costs, despite its high price.

Describing the new treatment as a "win-win" situation for consumers in controlling both hospital costs and the "worst pain known to mankind," FDA Commissioner Dr. Frank Young called it a "great medical advance."

About 100,000 Americans annually undergo surgery to remove painful kidney stones. The average operation costs about $6,700 and often keeps patients away from work for a month or more after surgery.

Those who undergo repeat kidney stone operations are at increased risk of losing a kidney.

Officials say the shock-wave machine potentially could replace 80 to 90 percent of current kidney stone operations.

Theoretically, about 100 units efficiently located around the country could handle about 80,000 cases annually, nearly paying for themselves with the savings in the first year and saving money in subsequent years.

The new machine is one of the most expensive single medical items ever marketed, with a price tag estimated at $1.7 million. But U.S. officials cited a Boston study suggesting that the device could save about $2,000 per case compared with surgery, partly by reducing hospital stays from one or two weeks to four days or less.

Heckler said she would ask the Health Care Financing Administration to make an "expedited ruling" concerning government payment under Medicare for the new treatment.

The lithotripter -- from the Greek lithos ("stone") and tripsis ("to crush") -- was tested on about 10,000 patients worldwide, 2,000 of them in this country, before winning government approval.

It is currently operating at six U.S. institutions that participated in the experimental studies, including the University of Virginia Hospital in Charlottesville.

The West German manufacturer, Dornier System, expects to sell 20 to 30 more machines in the United States next year.

Dr. George W. Drach, a University of Arizona urologist who coordinated the U.S. studies, called the lithotripter "a revolution in medical therapy." The machine directs shock waves, like a delicate jackhammer, at a kidney stone and shatters it into tiny grains without "doing any harm that we're aware of," he said.

Drach compared the action of the device to the shock waves generated by an airplane that breaks the sound barrier, causing "windows to crack and break."

The brittle kidney stones, accumulations of minerals and salts often as long as an inch, "vibrate in such a way that they fall apart," but human tissue and bones "have flexibility and give," he said.

Drach said the shock-wave therapy is suitable only for stones in the kidney or upper region of the urinary tract, not bladder stones or gallstones.

About 10 percent of patients may require additional treatment and, rarely, some still need surgery.

Side effects so far have been "very low," he said, "much less than 1 percent," primarily from blood clots around the kidneys that had no "serious consequences."

For lithotripter treatment, a patient is strapped into a reclining seat and lowered into a stainless steel tub filled with water. Anesthesia is administered to control pain, but the patient usually remains conscious. Two X-ray devices on each side of the machine are used to help locate the stone, Drach said.

Between 200 and 400 shock waves are needed to begin breaking up the stone, but a complete session of as many as 1,500 shock waves over an hour may be required to pulverize it into tiny particles that later pass out through the urinary tract.

A patient can listen to music to block the sound.

Gary Geniusz, 37, a government employe here who was one of about 200 patients treated in Virginia, said he heard a noise "like a bang" but noticed "very little feeling at all" during the procedure. He was out of the hospital in three days and back to work in a week.

Surgical removal of his first kidney stone left him "practically an invalid for at least eight weeks," he said.