Sgt. Joseph Bisbing, an assistant supervisor at a Philadelphia subway station, was one of the first marines off the enormous green helicopter that landed here to attack the National Guard at dawn this morning.

Automatic rifle swinging at his side, Bisbing rounded the tail of the CH-46 behind a heavy screen of white smoke, then retreated to the grassy woodland about 50 feet away. Several minutes later, he and 89 other marines charged out of the woods screaming and firing their rifles at about 200 National Guardsmen perched in a nearby encampment.

With a look in his eye that reflected all the seriousness of war, Bisbing dived over the barbed wire that protected the enemy.

The battle, at that point, was won.

"If I wasn't here today, I'd probably be doing some work around the house or watching television with the wife," said Bisbing, who traveled to the Delaware shore to take part in the first ever joint services "war game" on the East Coast.

Bisbing and most of the other reserves who grunted their way through the exercise are "weekend warriors" who pick up their rifles two days each month. Most of these lawyers, factory workers, cabdrivers, auto mechanics and insurance salesmen had never before seen the likes of even simulated war. Many of them had never flown in a helicopter before.

They had little more experience, in fact, than the 300 or so tourists who came over from the nearby shore resorts to watch the dawn invasion.

Indeed, the one thing that struck these part-time soldiers was that, as Bisbing put it, "everything seemed so real." Some enjoyed that, others did not.

"I like wild adventures like this," said Pvt. Sonny Coles of Philadelphia, an auto mechanic. "It's great experience. The only thing that I'd change about this whole operation is the location. I'd like to fight out in the desert."

However, to Lance Cpl. Althesine Phillips, a truck mechanic for the Marine division, the exercise was "a very traumatic experience."

I'm no women's libber," said Phillips, "but I'd never sign up for a real war."

The three-day drill, code-named Operation Liberty Four 79, was designed to simulate war situations in a convoy. The only Navy ship involved in the exercise, the USS Charlestown, was to be escorted by an imaginary squadron of destroyers, antisubmarine helicopters and minesweepers.

Upon reaching the imaginary destination of Rotterdam, in this case Bethany Beach, the Charlestown would be forced to deploy a band of marines who would clear out a tiny enemy outpost occupied by the National Guard.

There was some evidence to show that the D-Day shift was not quite ready for war. The five-man reconnaissance outfit that parachuted from a helicopter onto the battlefield had difficulty hitting its target. Three of the men ended up in a marsh on the other side of the target field. The commanding officer, who jumped last, barely missed a tree in the back yard of a Bethany Beach resident.

The delay involved in retrieving the wayward parachutist forced the joint command to cancel the strafing of the helicopter landing field by F-4 Phantom jets. When the commander, an insurance salesman, returned, he said the group's timing had been thrown off when the first parachutists took the directions "right now" to mean "one minute."

But even with these mistakes, the war game was taken seriously by the commanding officers. Rear Adm. Thomas Loughran, who commanded the combined forces of the Navy, Marine Corps, National Guard and Army, said at the end of the Battle of Bethany Beach: "I believe we'll try to do this again next year. It gives the reserves firsthand experience in the field."

Loughran, a lawyer, had noted earlier that even when reserves participated in war games in camp, they were forced to use the most outdated equipment. "It's difficult to train soldiers when the equipment is 20 or 30 years old," he said.

The four-hour Sunday morning battle was not without its costs. Although the ammunition was not live, one soldier had the top of a finger blown off when he attempted to pick up a smoke cannister that had failed to go off. CAPTION: Picture 1, "Weekend Warrior" crosses barrier during war game attack on an enemy encampment. Photos by Lucian Perkins - The Washington Post; Picture 2, Guardsman awaits attack as spectators watch.