The owners of Arlington's cable television franchise are launching a crackdown on residents who have been illegally tapping into the system, causing the cable firm to lose an estimated $740,000 in revenues this past year alone.

Although the firm, Arlington Cable Partners, has prosecuted a handful of violators in the past, Christopher Young, ACP's vice president of operations, said: "Our goal is not to prosecute people, but to convert them to paying subscribers."

"They have demonstrated to us their desire to have cable television," he said.

Young said that if ACP discovers that a resident has hooked into the system without paying, the company simply will approach the individual and ask him to pay.

If the request is denied, he said, the company will disconnect the service.

Young said that the firm will take legal action against the individual if he illegally hooks up a second time.

According to John Evans, the president of the company, about 32,200 of the county's 75,000 homes subscribe to the 35-channel system and about 3 percent of the total households receive the cable service illegally.

This 3 percent includes both those who break into the system from scratch and those who subscribe to the company's basic cable service and then illegally tap into one or more of the four extra-charge channels: Home Box Office, Playboy, Walt Disney and Cinemax.

Arlington's cable snatchers will find their illegal activity more difficult this coming year, thanks to the cable firm's plans to spend more money to detect cable thievery and to new federal legislation outlawing cable stealing, which takes effect Dec. 29.

The maximum punishment for cable theft by an individual, a criminal offense, is one year in jail and a $1,000 fine in Arlington, which has had cable television for more than six years.

Cable snatching is a growing nationwide problem, according to Edward Dooley, vice president of public affairs for the National Cable Television Association, the industry's major trade association.

"This is no longer a joke," Dooley said. "The problem was sort of laughed at at first. But the scope of it is quite staggering. As the industry grows, the scope of the problem grows."

Nationwide in 1983, he said, the cable industry lost between $300 millon and $400 million in revenues because of cable snatching.

Dooley said in the past year, the lost revenues have ballooned to between $500 million and $700 million.

Although 32 states, including Virginia, have laws barring cable theft, the new federal legislation is expected to make it easier to prosecute violators because it clearly states that the stealing, manufacturing and distributing of cable equipment is against the law, Dooley said.

At the same time, the new legislation offers cable companies in states such as Virginia another way to combat the problem, he said.

"It's another iron in the fire for us," Young said. "It gives us another avenue for prosecution."

Young said that his company has spent between $5,000 and $7,000 this past year in "tap audits" to detect illegal users and plans to spend four times that much for this purpose in 1985.

At the same time, Arlington Cable Partners president Evans said that he plans to meet soon with Arlington's Commonwealth's Attorney Henry Hudson to discuss strategies for prosecuting cable thieves, so as to take full advantage of the new federal legislation.