Early in the afternoon a small group of marines,some swathed in makeshift bandages, stumble from a helicopter touching down at a command post in Virginia.

The group is part of a graduating class of second lieutenants in training at the Basic School at Quantico, Va. The "wounded" men staggering from the plane are only faking it. But 10 minutes away, back at the base, the commander of what used to the Quantico Naval Hospital is worried nevertheless.

Quantico Naval Hospital, which serves some 10,000 soldiers-in-training and their families, was changed to a clinic early this summer. That means it lost its "billets," i.e. the right to have four surgeons and 32 hospital beds. Now it has no surgeons or hospital beds. That's what's worrying Cmdr. Jim Erie.

"We've lucked out so far," since the hospital was scaled down June 15, Erie said last week, "We've not had any major trauma. But it's bound to happen. We're going to have a very serious injury, and the patient might lose his life."

Erie worries about what might happen if someone was badly injured somewhere on the 64,000-acre base. He estimates it would taken an extra 20 minutes to get the person to the nearest operating room, at Potomac Hospital in Woodbridge, about 12 miles away.

"We could patch 'em up here, hold 'em together, but we have no operating room or surgeon. So what about people who can't really be moved?" Erie asks.

Erie words last week were faintly prophetic. Two days later, two marines were killed when their helicopter crashed and erupted in flames 500 yards from the simulated command post. The marines, caught in the buring helicopter, were declared dead at the scene.

"If they'd been alive, if they'd been brought down here, I'm sure our guys would have given them a fair shake," Erie said " . . . but I don't know. It's this kind of thing we're afraid of."

The hospital at Quantico is one of four military medical facilities across the country that have been scaled down this year to save money. Of six military hospitals evaluated for their efficiency last year, those at Quantico, Annapolis, Key West, Fla., and Port Huenene, Calif., got the ax.

The Bureau of Medicine and Surgery of the Department of the Navy (BUMED) determined that changing the Quantico hospital to a clinic would save $1.3 million to the Department of the Navy and $400,000 to the Department of Defense.

But Rep. Herbert E. Harris II (D-Va.) has challenged those figures, and last month requested a review of the BUMED study by the General Accounting Office. That investigation began last week.

Harris asked if the estimated savings were realistic in light of the increased costs of coverage for the use of nonmilitary medical facilities. He noted that some hidden expenses might accrue from the lost work time and gasoline spent traveling to outlying facilities as far away as Bethesda.

Harris said he also worries about the reduced emergency facilities. "Patch-up jobs are inefficient and I think quite dangerous. And they might just make the decision to keep the person in a back room for fear of transferring them, which could also be dangerous," Harris said.

Capt. James Quinn, of BUMED's policy and programs department, defended the decision, which he recommended last year.

"There's always the possibility of problems developing everywhere, whether you go across the street or whatever. But when we weighed out what we had, we felt it was a good decision," Quinn said.

The BUMED study cited Quantico's "low patient workload" as reason for the action.

The hospital treated 1,205 "true" emergencies this year so far, and 2,124 last year, according to Lt. Cmdr. Don Wilson, director of administrative services. "True emergencies," he said, include "bad fractures, head injuries and auto accidents."

Maj. David Ingram, who fought in the war games last week, said the base's accident record "is very good, considering what we do."

According to Erie, marines-in-training at Quantico practice firing live ammunition "from everything from small arms to surface-to-air missiles."

Ingram, 34, also was concerned about the added inconvenience to his family of having to travel to civilian hospitals.

"We had a child born last month and had to go all the way to Fredricksburg," he said. "Besides, you just feel a little better in a military hospital."