The Arlington County Board unanimously passed a law yesterday empowering county police to use the "Denver boot" on cars with three or more outstanding parking tickets.

County officials said that within the next three months owners of cars registered in the District, Maryland or Virginia with three or more Arlington tickets will receive letters notifying them that they risk "immobilization" of their vehicles if their fines are not paid.

Officials said they expected police to begin placing the boot on cars with the next few months. Arlington is the second jurisdiction in the metropolitan area to permit use of the boot. The District of Columbia also uses a boot.

"People just laugh at these parking tickets," said County Attorney Jerry K. Emrich in urging the board to adopt the ordinance. "We recently towed a car with 50 outstanding tickets," he said, noting that booting cars is less expensive than towing them.

"Frequently if a car is towed the owner doesn't know what's happened to it," said County Manager W. Vernon Ford. He noted that because Virginia has no reciprocity with other states, Arlington has been unable to collect parking fines from drivers with out-of-state license plates. By using the boot, however, Arlington police can immobilize an offender's car until he or she pays the tickets.

Most of the booting, Ford said, would be concentrated in the congested commercial sections of the county like Rosslyn, Crystal City and the streets near the county court house.