Washington Gas Light Co. customers in Virginia will get a natural gas rate increase for Christmas.

The Virginia Public Service Commission, which has been considering an $8 million boost in gas bills for nearly 18 months, is expected to act on the request shortly.

As soon as it does, Washington Gas Light will apply for an additional rate increase in Virginia, an attorney for the utility said yesterday.

Washington Gas Light, however, will have to wait at least until March for a decision on its request to start hooking up new customers in the District of Columbia.

The D.C. Public Service Commission yesterday adopted a schedule for hearings on the request, starting Feb. 8.

The gas company's request for higher rates in Virginia was filed in mid-1976. "We've been promised a decision by Christmas," a Washington Gas Light lawyer said yesterday.

PSC officials in Richmond said the final order on the Washington Gas Light request has been sent to the agency's legal department. They refused to speculate on when the rate case would be decided or how much gas rates would go up, but indicated some increase is certain.

The Virginia rate case has dragged on so long that another rate increase will be needed even if the company gets all it has asked for, the WGL official said.

Natural gas rates in other areas served by Washington Gas Light have gone up since the Virginia rate request was made. On Thursday the gas company got a $2.8 million increase in Maryland. Earlier this month it raised the price tag on a rate increase pending in the District from $8.6 million to $11 million.

Gas company officials have said the continuing increases in gas bills are one factor in the utility's revenue equation. The other is additional customers.

Washington Gas has asked to end a five-year moratorium on hooking up new customers by adding 10,600 new gas users, 3,000 of them in Washington and the remainder in the suburbs.

The main question in that request is how adding gas users will affect present customers, PSC staff attorney William McManus said yesterday as maneuvering on the request got underway.

He said D.C. utility regulators are also concerned about how these new gas customers will be allocated. Washington Gas Light officials have indicated they will hook up residential and small commercial users on a first come, first served basis.

But Public Service Commission members yesterday indicated they want special priorities for inner city neighborhoods that were damaged by the 1968 riots.These neighborhoods have been exempt from the ban on new gas connections, but the proposal for adding new customers apparently would end their favored treatment, said PSC staffers.

D.C. officials questioned whether more of the new customers ought to be allocated to the city to encourage urban rather than suburban growth.

McManus said the hearings also will raise questions about how hooking up new natural gas customers jibes with national energy goals. Conserving energy and shifting from scare fuels - like natural gas - to more abundant ones are among President Carter's priorities, he noted.

Regulators also questioned whether existing gas customers should have to bear any costs of expanding Washington Gas light's service to new customers. Gas company officials said they assume the new customers and the expense of serving them will be "rolld in" to present gas rates, rather than charged special fees.

PSC members raised the issue of whether present gas customers should have to pay for an advertising and promotion campaign to get new gas users.