A SURGEON SITS IN his comfortable Washington office. After a long interview, he begins to tell a seemingly unrelated story about medicine and Vietnam:

In the late 1960s, a 19-year-old American soldier with a three- inch-long mortar shell in his skull was hurried into a Navy hospital in Vietnam.

"We X-rayed it," said the surgeon, who was on duty at the time. "The brain was cut off from the spinal cord . . . He was breathing. His heart was beating . . . the mid-brain was still working, but he was decerebrate."

"I had two neurosurgeons on the staff examine him. We had to make a decision whether to go after that shell or leave it alone. They said that for all intents and purposes, the boy was a heart- lung machine, that his brain was hopelessly destroyed."

The neurosurgeons did not want to operate, he recalled, because ty were afraid the mortar might explode in the operating room. The surgeon called his boss. "He told me it was my decision."

He called the bomb disposal unit. "They came out to look at the X-rays we had taken and said it was live."

More patients were being brought in. The surgeon considered ordering his neurosurgeons to operate. He thought about attempting the operation himself with volunteers. He met with the emergency room staff once more. "I guess I was trying to just get support. I had to do something." He re-examined the soldier. The wounded man's heart was beating, he was breathing.

The surgeon suddenly stops telling this story. He sits silently for several minutes.

"I think of all my experiences, that episode has brought me the most sorrow," he says. "What happened was that we took the boy out to this bunker behind the hospital and plastic explosives were put on his scalp."

The surgeon watched the bomb disposal squad attach the putty- like charge. They worked fast, expertly, he recalled. The wounded man's face gave no sign that he understood what was happening. The surgeon said a prayer for the soldier -- and himself.

"It was detonated. There wasn't much left. The mortar had been a live one."

The surgeon wipes tears from his eyes. His voice is hoarse.

"It was a goddamned war!" he said. "A goddamned war!"

THE BIGGEST ADVANCE in emergency care to come out of the Vietnam war involved transportation, not medicine. In previous wars, armies had to move field hospitals as close as possible to the fighting. In Vietnam, helicopters plucked wounded soldiers from fire- fights and delivered them to operating rooms in an average round- trip time of 30 minutes.

During World War II, nearly one- third of Americans hit by enemy fire died. In Korea, one of every four Americans hit died, and in Vietnam, only one of five hit died, even though the high-velocity, rapid-fire rifles used on both sides caused multiple injuries.

The military used two-seat helicopters in Korea to carry wounded strapped to the chopper's side. In Vietnam helicopters became "air ambulances," large enough for two pilots, a mechanic, paramedics, emergency equipment and six to eight wounded.

The "Hueys" used in Vietnam were faster, stronger, more versatile and more reliable. They had to be. Medical helicopters were hit 50 percent more often than combat helicopters because they often landed in the middle of enemy fire.