The Potomac Electric Power Co. has asked the Maryland Public Service Commission to grant a nearly 9 percent reduction in the fuel billing rate for Maryland customers, the utility company said yesterday.

The proposed 8.8 percent rate is the lowest since December, 1984, company officials said.

The request, to be effective with bills starting Oct. 1, would reduce the current fuel billing rate from 1.964 cents to 1.791 cents per kilowatt-hour for Pepco's residential and commercial customers in Montgomery and Prince George's counties.

The proposed reduction for the typical Maryland residential customer would mean an average savings of about $1.34 a month, based on 773 kilowatt-hours of use.

Edward F. Mitchell, Pepco president, said the trend in lower fuel costs can be mainly attributed to lower costs for fuel; lower transportation costs of coal to Pepco's power plants; high efficiency at the company's coal-fired generating plants, and transactions with other utilities that saved customers an estimated $18 million in fuel costs last year.

Mitchell also noted that savings have occurred because Pepco this summer began buying and receiving capacity and associated energy from Ohio Edison Co. and Allegheny Power System under a recent long-term agreement.

The agreement enables Pepco to add generating capacity at a cost substantially lower than the cost of building new facilities, company officials said.