It has been six months since trucks were banned from the left lanes of much of the Capital Beltway, and state police in Maryland and Virginia say the ban -- aimed at reducing accidents -- is being obeyed by most truckers.

Statistics are still being compiled.

But state police in both states said they expect they will show some reduction in the number of accidents involving trucks.

The restricted portion of the Beltway stretches from Georgia Avenue in Silver Spring to the banks of the Potomac in Prince George's County, across the Woodrow Wilson Bridge and through Alexandria to the Shirley Highway (I-395/I-95) interchange in Fairfax County.

The ban was put into effect Dec. 1 as a one-year experiment. According to American Automobile Association figures collected in 1983, trucks were involved in 16 percent of Beltway accidents, although they constitute only 4 percent of the traffic.

Lt. Mike Barnes of the Maryland State Police said troopers there stopped 67 trucks for driving in the restricted left lanes from Dec. 1 through the end of April. Most of these trucks -- 46 of them -- were stopped in December, he said; in April, only four trucks were cited for driving in the left lanes.

"We consider that a very low number of violators," Barnes said. On citizens' band radio, he said, police hear "a lot of conversations back and forth between truckers, that they are approaching truck-lane restriction. That's really helping us out."

Barnes said police have not yet obtained data on accidents involving trucks in the restricted portion of the Beltway. "But our day-to-day experience is showing that there doesn't seem to be as much involvement with the big trucks," he said.

The penalty in Maryland for violating the left-lane restriction is $30. Penalties of up to $1,000 are possible in Virginia, but state police expect them to average $50.

Figures on violations were not immediately available in Virginia, but state police there said there have been few violations.

"The compliance has been right well, considering the amount of truck travel on that road," said Sgt. K.R. Redden. "We haven't had any complaints about the problems of enforcement, and we haven't written up that many violations."

Mary Ann Reynolds of the American Automobile Association said police have reported a good rate of compliance, but automobiles appear to be driving faster in the Beltway's left lanes now that the trucks are gone.