A coalition of Maryland consumer groups is seeking 10,000 customers of the Washington Gas Light Co. who will pledge to withhold payment of part of their gas bills.

The purpose is to show the Maryland Public Service Commission that there is widespread opposition to the innovative "system charge" it ordered for the gas company last November.

The system charge is a basic fee each customer must pay monthly and is not related to the amount of gas used. It is supposed to pay most of the company's fixed charges for operations and administration, guaranteeing the company a steady annual income.The company thus does not have to depend on customer usage patterns.

The system charge plan is the only one in the country, according to spokesmen for gas company and the commission. Public Service Commissioner Michael Darr Barnes said the commission has gotten favorable comment about the plan from consumer groups in other parts of the country, but all it gets from Maryland activits are brick-bats.

The Maryland Action Coalition, consisting of about 75 groups, organized the pledge drive. It hopes to present the pledges to the commission and force a reopening of the issue. Only the system charge would be withheld from payment if the coalition asked people to honor their pledges.

Many members of the coalition maintain the system charge is unfair, has caused heavy increases in consumer gas bills, and discourages rather than encourages conservation of natural gas.

The commission and the gas company counter that gas bills have increased because of a rate hike of 10.92 per cent, greater usage during the cold spell and higher prices for natural gas from suppliers.

"The idea of people withholding part of their gas bill payment is unfortunate. The trariffs are legal and were arrived at with the procedures we use under our democratic process," Barnes said.

"People simply don't understand the system charge. They seem to think it is an extra charge added on to their bills. It is not. If we abolished it, the same amount of money would have to be put back into the rate system," he said. "At present everyone is paying a flat charge of 20.73 cents per therm (100 cubic feet) of gas. Without the system charge, the gas rate would be much higher - maybe 26 or 27 cents per therm."

Barnes conceded that the consumer activists had a point in criticizing the system charge as not encouraging conservation.

"It is true that some customers are paying more as the result of the system charge," Barnes said, "but those are people who were in effect subsidized by other customers before."

Those being brought up so higher levels of payment are generally small users - small businesses and small usage households, he said.

The Commission set across-the-board system charges as follows: $8 for residences using gas for heating or cooling and $4.15 for those using gas only for other purposes; and $22.50 for all commercial users of gas for heating or cooling and $15 for users of gas for other purposes only.

Barnes said that he is now convinced that in practiced it isn't fair to ask the small users to suddenly begin paying the larger charges and that some adjustments are going to have to be made in the system.

Barnes said he hoped citizens would not withhold partial payment from their gas bills and instead attend "an informal consumer conference" to be held in the County Council chambers in Rockville at 8 p.m. May 24.

"If they withheld payment from WGL," Barnes said, "they might force the company to ask for another rate increase."