The Arlington County Board yesterday voted to deregulate the Washington area's first major cable television system, brushing aside objections by subscribers and the county staff that company officials are unresponsive and have yet to fulfil their promises for the system.

The decision to deregulate the rates of ARTEC (Arlington Telecommunications Copr.), which began operation in 1978, comes nearly four months before wiring of the $8 million, 27-channel system is scheduled to be completed.

Because it is the first countywide system in the metropolitan area, ARTEC's progress is being watched closely by officials in other jurisdictions where cable systems are under construction.

Yesterday's action means that basic service to the 13,000 Arlington households that now subscribe will be raised $2 a month, to $10, beginning sometime this fall. Installation fees and fees for Home Box Office, an extra entertainment programming feature, will be unaffected.

The decision also reserves for the board the power to resume regulation if that is determined to be in the public interest.

"It's clear that they're not responsible to the public," said Joseph Lewis, a subscriber who spoke against deregulation. Lewis said that some 20 phone calls and several letters to ARTEC about service went unanswered. "I don't think they have reached the maturity to be left alone," Lewis said.

But officials of the franchise argued successfully before the Republican-dominated board that "the Arlington marketplace is the most efficient price regulator," ARTEC president, Thomas W. Richards, a former county board chairman, and chief operating officer John D. Evans told the board that a rate increase was necessary because of increased operating and programming costs.

Although ARTEC's books are closed, county figures show that the company is expected to earn gross revenues of $3.7 million this year, more than double last year's amount. Cable systems are traditionally expensive to start up and rarely show a profit for the first eight years of operation, according to those in the industry.

County consumer affairs chief Charles Hammond, an opponent of deregulation, recommended instead that the county grant a montly rate increase of $1. Hammond reminded the five-member board that ARTEC had yet to meet commitments agreed upon in 1973 when the franchise was awarded. These include provisions that the company provide a fully equipped studio and teach classes for residents interested in producing programs.

"Many public spirited people feel that the only real (clout) the county has is economic," said Hammond. "One of the weakness in the franchise agreement is that there are no deadlines" by which ARTEC must meet its commitments.

Richards assured board members that ARTEC would honor its promises, but said that completing the wiring of the county was ARTEC's first priority. In response to complaints that officials are unresponsive, Richards said, "We're not out there on Wilson Boulevard scheming to deny customers service."

"I am persuaded that the market place will be effective as a regulator," said board member John W. Purdy. "ARTEC is not really a monopoly, they have cometition." The company has an exclusive contract with the county, scheduled to expire in 1983.

Board member Dorothy T. Grotos cast the lone vote against deregulation, saying that to do otherwise would "disregard the community's feelings."