The Maryland Public Service Commission yesterday gave Washington Gas Light Co. a 2.1 per cent increase in natural gas rates for its customers in suburban Maryland.

The higher rates will mean its Maryland customers will pay an additional $2.8 million a year for gas heating and cooking, the company said.

The 2.1 per cent increase amounts to an additional 87 cents a month on the average bill for Maryland gas heat customers of $41.51.

It will cost customers who only cook with gas about 25 cents a month on their bills, which now average $12.19.

The increase granted by the Maryland utility regulation agency was short of the 3.2 per cent that Washington Gas Light has asked. The company said the increase was needed to maintain a 9.25 per cent increase return on its investment in the state.

Commission officials were not available for comment on the rate increase, which was granted under a new Maryland procedure giving utilities virtually automatic rate increases to maintain their return on investment.

Gas comapny spokesman said they were uncertain about exactly when the new rates would be put into effect, but said it would be soon.

The Maryland increase came less than a week after Washington Gas Light boosted its request for higher rates in the District of Columbia.

Citing the same arguments used in Maryland - declining return on investment - the utility raised its request in the District from $8.6 million a year to $11 million.

Washington Gas Light is also seeking to increase its revenues by starting to hook up new customers after a five-year moratorium.

The D.C. Public Service Commission will hold hearings Tuesday on the request to expand gas use. Maryland's utility regulators have already started hearings on the subject.

The gas company's plan to resume expansion by adding 10,000 new customers in Maryland, Virginia and Washington is being fought by Potomac Electric Power Co.

Since the moratorium on new gas hookups was imposed in 1972.Pepco has had a monopoly on new customers.

Some $5 million a year in customer's heating and cooking bills are at stake in the dispute between the two utilities.