Colonial Transit Co. Inc., a private firm that provides commuter bus service to Washington for Reston residents, ordered its drivers to avoid the George Washington Memorial Parkway Wednesday after some buses were ticketed by U.S. Park Police for various violations.

Charles Kenny, executive director of transportation for Clolnial, confirmed yesterday that drivers were instructed to stay off the parkway. "In two days we had two sets of buses pulled over," Kenny said. "We don't need that. So we're in the process of getting with the proper people to find out what the problem is." Some of the buses returned to the parkway yesterday, Kenny said.

George Berklacy, a spokesman for the Park Police, said Colonial's buses were not banned from the parkway, through any police action, as some Reston commuters said they had been told.

Berklacy said that about a dozen Colonial buses have been cited by Park Police in the past month for violations ranging from excessive exhaust fumes to slick tires. "Theres no campaign on," Berklacy said.

Colonial, which is based in Fredericksburg, won the Reston service contract two years ago after a protracted and bitter regulatory fight with Metrobus. The Reston commutor service carries about 1,300 passengers a day between the Fairfax County new town and various points in Washington. There has been a growing number of complaints about the Reston service from its users.

Kenny said, and regular riders confirmed, that Reston buses frequently are routed around the Beltway and into Washington via Shirley Highway instead of along the parkway, depending on traffic.