The Virginia Supreme Court yesterday made it harder for police in the state to arrest motorists because they have radar detection devices, commonly called "fuzz busters," in their cars.

It is still illegal to use or sell the devices in the state, but the court, in a unanimous decision, said the state has to prove that the device was being operated before the motorist can be charged with violating the law. Virginia is the only state in the nation specifically to outlaw radar detection devices.

"It going to be tougher to enforce the law" said Virginia Attorney General J. Marshall Coleman Jr.

"The motorist will have to be caught in the act" of operating the radar detection device, said Albert M. Orgain IV, who represented the five persons whose appeal of their convictions to the hight court resulted in yesterday's decision."It just makes it hard to prove," he said.

The court, which reversed the convictions of the five persons, overturned a section of the state law that allowed police to charge motorists with violating the law merely on th basis of the presence of the radar detection devices in their cars.

Virginia state police have maintained that the only purpose of the detectors, which blink, buzz, or whistle when they detect the presence of radar used to detect speeders, is to enable drivers to speed above the posted limit.

Truckers have complained of being stopped by police who search the cabs of their trucks for the "fuzz busters," which normally are mounted on the dashboards when in use. Travelers from the other states have found themselves under arrest once they cross into Virginia.

The devices, which cost form $100 to $150, have been confiscated by police.

The last session of the Virginia General Assembly passed a law enabling drivers who are arrested and convicted to get their detectors back if they request them and pay the mailing expenses. Under the same law, which goes into effect July 1, drivers who have a detector in their car but do not have it hooked up could not be arrested.

Orgain said his five clients, four of whom were from out of state, were charged with violating the law in 1976. He said their "fuzz busters" were taken by the police and they were fined $25 to $100.

Because of the court ruling Orgain said his clients will get back their radar detection devices and will have to pay the fines.

"It's a victory for us," said Orgain, a Richmond lawyer. But, he added, "It's still illegal to use one ('fuzz buster'), to equip your car with one or to sell one."

He said he believes that if a motorist had a radar detection device on the back seat of his car it would be difficult for state police to charge him with violating the law.

Coleman disagreed. The attorney general said, "He's (a state trooper) got him (a motorist), if the detector is "somewhere accessible" and is in working condition.

"What you need to do if you're driving through Virginia," Coleman said, "is put it (your 'fuzz buster') in the truck of the car."