North Arlington residents served by the Potomac Electric Power Company will be paying higher electric bills, if a 21 per cent increase requested Monday by the company is approved by the State Corporation Commission. The increase would provide Pepco with an additional $3.18 million in annual revenue.

The rate request, the third in as many years, would affect about 2,300 residences in a three-square-mile area of Arlington which includes the Pentagon. Pepco spokesman John Grasser said that if the request were granted, residential customers would pay $16.74 in the summer for 250 kilowatt hours of electricity, an increase of $2.95. Winter rates for the same amount of electricity would be $16.46, an increase of $2.88.

Pepco was granted a similar 21 per cent rate increase in July 1976. Grasser said of this latest request, "The rates that are in effect now are based upon a 1975 test year. This is 1977, and we all know what inflation has done. The rates are just outdated."

Before a decision is made on the rate request, the State Corporation COmmission will hold a pre-hearing conference in Richmond where Pepco spokesmen and customers can present testimony.