More than 150 persons stood on a runway at Andrews Air Force Base for almost two hours yesterday, watching large trailer trucks skidding along a surface into yellow, rubber cones.

The reason for this rather unusual assemblage was a demonstration of how well a special air brake antilocking device keeps trucks on the road and going in a straight line even under quick, emergency stop, situations.

The Heavy Duty Vehicle Brake Council was the host, using some 40 different demonstration runs to show that the special antilock braking system can and does keep a truck in a straight line.

The antilock system prevents skidding by automatically modulating the amount of air pressure getting into the air brake system of a truck. The system activates whenever it senses the wheels are about to lock up, as in a skid situation.

"They worked the way they were designed to work," said Joan Claybrook, head of the National Highway Traffic Safety Administration and a longtime supporter of standards mandating the use of such systems.

In fact, in 1975, Federal Motor Vehicle Safety Standard No. 121 - Air Brake Systems - was put into effect. That rule mandates that all newly manufactured trucks be built with braking systems that can stop a vehicle traveling 60 miles per hour within 293 feet - without any loss of control. It was vigorously opposed by several trucking groups.

Virtually all heavy vehicle manufacturers chose an electronic antilock system to meet that performance standard. But the standard was challenged in a wide-ranging legal action brought by trucking organizations in the Federal Ninth Circuit (California).

The district court took more than three years before ruling that NHTSA had not adequately overseen the operation of trucks using antilock systems. The case is under appeal to the Supreme Court, which may hear it this spring.

Transportation Secretary Brock Adams is reportedly considering softening the existing rule by only requiring antilock devices on the tractor, and not the attached trailers. He also is considering a moratorium on enforcement of the 121 performance standard until the Supreme Court finally rules.

The real purpose of yesterday's demonstration may have been an attempt to convince Adams, who was there along with Claybrook and about 50 other DOT personnel, that the trucks need antilocks on all axles, including the trailers.

In one test, for example, a truck with no antilocking device skidded into a Z shape, while a truck with antilocking devices on truck and trailer came to a straight stop.

Finally, a truck with antilocks on just the tractor found itself skidding into the same Z pattern as the truck with no antilocks at all.

"That was the most important lesson of the day," said a Brake Council spokesman. "I hope our lesson was not lost on Secretary Adams."