The D.C. Public Service Commission said this week that it may require Washington Gas Light Co. to transport, rather than sell, gas to customers who request it, making it possible for some large District of Columbia customers to be supplied by other companies.

The commission issued an order in which it said it would look at the transportation idea in the spring, together with other issues, when it explores Washington Gas' request for a 9 percent rate increase.

Washington Gas serves about 143,000 customers in the District, of its total of 582,000 customers in the District, Virginia and Maryland. Last October, the company asked to raise rates in the District by $16.4 million. The company said it needs the money to cover rising expenses over the past three years.

The increase, which must be approved by the PSC, would raise the average bill by $7.10 a month for a residential heating customer using 1,173 therms annually. For a residential nonheating customer using 91 therms annually, the monthly increase would be about $1.20.

As part of the rate case, the PSC said it will investigate whether all utilities in the District, including the Potomac Electric Power Co., are purchasing and supplying energy at the cheapest cost.

The commission also is examining whether it can compel Washington Gas to develop a rate for transporting as well as distributing gas because of a controversial new set of federal rules meant to establish new gas supplies, increase competition and lower natural gas prices.

Under a ruling issued last October by the Federal Energy Regulatory Commission, pipeline companies are being asked to change their role as buyers and sellers of natural gas to include transporting natural gas for customers like Washington Gas or large commercial customers that can buy directly from suppliers.

Columbia Gas Transmission Corp., the Charleston, Va., pipeline subsidiary of Columbia Gas System Inc. that serves Washington Gas, has volunteered to be a transporter for interested customers.

The PSC also will examine whether it is proper for Washington Gas to ask customers to pay the expenses of certain programs of the industry group Gas Research Institute.

Whether the new reorganization of Washington Gas will affect District rate payers also will be examined.

In August, the company created three new divisions to serve separate jurisdictions -- D.C. Natural Gas, Northern Virginia Natural Gas and Maryland Natural Gas. The D.C. Office of the People's Counsel, which represents rate payers before the PSC, has been concerned that splitting up the company could lead to "inequitable" treatment of D.C. customers.

The PSC also will study whether Washington Gas's ability to raise or lower gas rates to large customers that can switch from gas to oil doesn't adversely affect customers who pay a fixed price.

Lastly, the PSC will decide whether to create a special, lower gas rate for low-income customers.