SAIGON — "Hey, captain," the sergeant said with the disinterested, matter-of-fact calm of a professional. "look at this."

The young navigator looked, and at last had time to be nervous — perhaps even a little afraid.

In the door the crew used to get in and out of the C130 transport plane was a small hole — the kind a vandal might make in a door with a sharp piece of metal. There was a jagged rent in the other side of  the door and an even larger hole in the metal cabinet directly behind the navigator's chair. The sergeant searched carefully and pulled a spent, mangled 7.62 cal. bullet out of the visor on an altimeter. It was only eight inches from the headrest on the chair.

Now Capt. Gary M. Davis, Bernie, Mo., was pale and reflective. His hands shook a little and lie made nervous fumbling movements as he left the plane and stepped onto the concrete floor of the revetment at Tan Son Nhut.

"I think I'm lucky," lie said to a bystander. "I think we're all lucky. That could have hit anybody."

He pocketed the bullet before he walked away — a souvenir of a daylight nightmare he likely hadn't seen the last of.

Others in the 374th Tactical Airlift Wing stood outside that aircraft or their own, laughing, joking, trading stories — the kind of buoyant, let-it-all-hang-out relief that follows what the Air Force calls a "high risk" mission. And this one had been high risk indeed. An hour or so before, four of the giant transports had thrust themselves low, very low to drop food and ammunition — the means to live and fight — to the ARVN garrison holding the besieged provincial capital of An Loc.

Besides a North Vietnamese rifleman's lone, game effort to bring one aircraft down with a single shot, there had been 51 cal., machine guns and 37 "mike mikes" — portable, devilishly accurate little weapons that poured up a glittering volume of fire, comparable to anything American pilots faced at Schweinfurt and Ploesti during World War II.

On Davis' plane, gasoline poured from a ruptured fuel line and a red crash truck rolled out to hose it down.

"Man," said Sgt. Walter W. Warner of Covington, Ky., who was loadmaster on one of the transports, "we were so low I could see squirrels in the trees."

He wanted to talk to somebody, anybody, about anything. He pulled off the go-to-hell hat he sports, showing a peace sign that had been sewn on the crown, and an assortment of trinkets that included tiny metal chevrons of a Marine corporal and an Army sergeant. Inside the hat was a first lieutenant's bar.

"That's my real rank," he joked. "I'm just posing as a buck sergeant." He promised others — and himself — a rousing night at the club. He allowed that this mission was not as had as another that had been run at night — with 60 holes counted in his aircraft.

During Thursday's mission, other pilots and crew members explained, they did everything by numb, professional reflex — there was no tine to be afraid. Now there was tremendous relief and allowable tension.

There had been An Loc again — first an indistinguishable smear of smoke, then a broken little civic corpse, Three of the planes dropped their loads on target, to friendly lines, or close enough to be recovered. Capt. Bruce A. Bleakley had to abort his drop, explaining that his navigational equipment had malfunctioned and he had to swing wide of the town. lie could not bank and correct his approach — might. have jabbed his wingtip into the ground.

It was Capt. William L. Calhoun's first combat drop — the moment-of-truth payoff he had trained for the past three years. Thrusting out of cloud cover at. 4,000 feet, into a flashing galaxy of fire, he recalled, "there was not enough time to think about it. Everybody was too busy doing everything."

The issue was still in doubt at An Loc, and Calhoun, Davis, Warner, Bleakley and the others know they hadn't seen the last of it.

"I'm glad to have that first one behind me," Calhoun said. "It won't get any easier, though."