Potomac Electric Power Co. proposed yesterday a $45.5 million rate increase for its customers in the District of Columbia.

In a petition filed with the city's Public Service Commission yesterday, Pepco said it is seeking average rate increases of about 16 per cent for all classes of customers.

Pepco also announced yesterday that it will seek higher rates from regulatory agencies in Maryland and Virginia, but no details were provided on specific amounts.

Under the proposed rates, basic residential service customers in the District who consume about 500 kilowatt-hours of electricity each month would face a monthly increase of $3.34 on summer bills and $3.22 during the winter.

In addition, Pepco proposed a new rate schedule for recharging the area's relatively few electric automobiles. The schedule would be effective in off-peak hours - times of day when electricity consumption is at its lowest levels.

The company said the new rates are being proposed for residential customers "anticipating and, perhaps, stimulating such usage." Electric vehicles would have separate meters, and power could be consumed only between 10 p.m. and 8 a.m., at a kilowatt-hour rate about one-half cent lower than that proposed for peak, daytime use.

Pepco's rate increase proposal was filed less than a week after the utility posted a slight decline in profits for the April-June quarter of 1977. Profits dropped to 26 cents a share from 29 cents in the same period last year.

Pepco chairman W. Reid Thompson said yesterday that Pepco's operating and maintenance expenses will have increased 25.3 per cent this year over 1975, the year on which the firm's current rates are based.

Thompson said customer charges must be updated to reflect such costs and help Pepco maintain "a strong financial condition . . . without adequate (rates) the company's status in the financial markets would be damaged and its ability to provide reasonably reliable service to its customers impaired."

Pepco asked the commission to approve a 10 per cent rate of profit on its investments to provide service to the District, up from the current 9.06 per cent. That was the rate of return allowed by the commission when it approved a $29.4 million rate increase for Pepco last December. Pepco had requested a $52 million increase in December, 1975.

A rate increase of $21.4 million was approved in Maryland last January, and a $700,000 increase was approved in Virginia during mid-1976.