Arlington County, worried that its current system for towing wrecked, abandoned or impounded cars might be challenged in court, is switching from several to one private towing contractor and will give its towing business to the lowest bidder.

The move, the result of a year-old U.S. Supreme Court ruling, could mean that motorists who have their cars towed in the county will pay less to get them back than the $30 to $40 they are now charged.

Because of the court decision, Arlington, like other municipalities across the country, is revising the way it awards contracts to private businesses for public services. Next month, it will abandon its practice of awarding multiple towing contracts to businesses in different sections of the county and will award a new, two-year towing contract to just one business meeting upgraded standards and offering the lowest bid.

In a case involving Boulder, Colo., the court held that local governments do not have the automatic antitrust immunity of states and may be sued for violating federal antitrust laws when regulating cable television or any other private business activities.

"It was a shock for local governments," said R. Scott Wynn, assistant county attorney. "Now there is a new awareness on the part of local government that there is a potential for antitrust violations, which is not to say we were violating it under the old contracts."

In the past, Arlington officials said, the county divided up the towing districts to match the number of eligible bidders and set fees based on information supplied by the towers. With a current base rate of $30 for a daytime tow and $40 for nights, the estimated 8,000 cars that the police have hauled away annually is worth about $400,000 a year to the towers.

"One of the motivating factors for the change was the county's interest in introducing an element of competition or free enterprise into the process, to make sure the towing rates charged to people were the best rates possible," Wynn said.

But four small businessmen who have contracts with the county to tow cars say the court-inspired contract awarding revisions could cost them their towing business.

"After 50 years of providing good service, it's a hell of a way to treat a person," argued Bill Luzi, whose family has been towing cars in Arlington for half a century. Luzi's late father, Jitty, hauled off his first car for the county in 1932, and Luzi, 47, who also operates a service station in the county, had hoped to pass on the business to his 23-year-old son, Bill Jr.

"Why should this go outside Arlington County when we can perform the service here?" said Luzi, who complained that only large firms outside the county are going to be able to meet the new requirements.

The new towing contract, which county officials say is standard for most municipalities, requires that the bidder have six tow trucks for countywide operations, compared to the three now required of each of the four contractors. It also requires a refundable $2,000 to bid and a $20,000 performance bond if awarded the contract, in addition to providing lot space for 200 cars.

"We're not going to be able to compete," said George N. Prokos, another service station owner who now holds a towing contract.

Since the last contract was awarded two years ago, Luzi said, he has invested $42,000 in new and renovated equipment. If he loses the contract, as he expects, he said he will have to lay off four or five of his nine employes.