Arlington's cable televison system, which charges the highest rates in the Washington metropolitan area for basic service, has requested county approval for a 7.4 percent increase in charges.

The new rates, which would automatically become effective Jan. 1 if the County Board does not hold a hearing on the increase, have met with strong opposition from members of Arlington's cable television advisory committee, which is appointed by the board to oversee the operation of the system.

"I think these charges are just excessive," said Joseph D. Lewis, chairman of the advisory committee. "We did not expect an increase, and so far the company has not submitted justification for the request. If they don't do it, then I hope the rest of the committee will stand with me and say no."

The advisory committee will meet on Tuesday to discuss the issue, but it is up to the County Board, which has never refused to grant a cable rate increase, to approve the request.

"This is a marketplace decision, and I don't see why it would cause any objections," said John D. Evans, president of Metrocable, the company that holds the franchise to provide service to more than 30,000 households in Arlington. "The reality is that our customers demand service, and this is what we need to give the quality they have become accustomed to."

Evans said that strong sales of videocassette recorders are beginning to present competition to cable service throughout the metropolitan area.

The County Board will have the option of holding a hearing on the increase, which would raise basic monthly service costs for the 35-channel system from $13.25 to $14.20. Howard County's Howard Cable TV is close to the Arlington system in price, charging $11.95 a month for comparable service.

Recently enacted federal cable television legislation allows the automatic approval of up to a 5 percent annual increase in basic rates through 1986. After that, all rate regulations will be eliminated.

According to Lewis, a 7.4 percent boost would be twice the rate of inflation for a system that Lewis said has not incurred significant new expenses in the past year. It would be 43 percent greater than the 5 percent allowance mandated by federal law.

"I know there have been discussions, but I think we have pretty good cable service in general," said John G. Milliken, chairman of the Arlington County Board. "I just got the letter, so I haven't come to any conclusions yet. We would also like to see what the advisory committee recommends."

Several advisory committee members said yesterday that they were surprised that Metrocable had asked for the increase. Although several area cable franchises have been hurt by cost overruns and other problems, Arlington's -- which installed the first system in the region in 1978 -- has had relatively few problems.

"We get good service, there is no question about that," said Steven Berke, a member of the cable television advisory comittee. "We have largely avoided the crises we have seen elsewhere. But I didn't expect this to happen. I thought we were clear for a year or so."

Berke and other advisory committee members said they will reserve judgment on the cost increase until they can see why Metrocable believes it is necessary.