The Potomac Electric Power Co. yesterday moved to reduce the charge for fuel that it adds to customers' bills in Maryland.

Pepco asked the Maryland Public Service Commission for permission to cut the fuel rate charge by 5.1 percent--a reduction that would amount to a savings of about $1.17 on the average residential customer's monthly bill for 843 kilowatt hours a month.

Pepco said it was able to file for the reduction in the surcharge because of its increased purchases of cheaper power from utilities in the Midwest, where the recession has produced excess capacity. Pepco also said it has reduced its costs by burning more coal than oil and by buying relatively low-priced coal.

The reduction would decrease the fuel billing rate (a rate multiplied by the customer's consumption each month) from 2.738 cents per kilowatt hour to 2.604 cents a kilowatt hour. It would apply to the bills of the electric company's 325,000 residential and commercial customers in suburban Maryland.

If approved by the PSC, the rate would be effective for bills issued beginning on Nov. 29.

Pepco said that this is the first fuel rate change requested since June 1981.