Negotiators for Potomac Electric and Power Co. and Local 1900 of the International Brotherhood of Electrical Workers are returning to the bargaining table at 1 p.m. Friday at the request of the Federal Mediation and Conciliation Service.

Contract talks between the company and union had broken off at 6:30 p.m. Monday after federal mediators decided the two sides were too far apart on economic and related issues to continue negotiations. The impasse prompted strike threats from the union, which the company met with increased preparations to deliver service to its customers in the possible absence of 3,500 unionized employes.

Pepco, an investor-owned company, serves 525,204 customers, 89.8 percent of them residential, in the District of Columbia, and in Montgomery and Prince George's counties in Maryland, and in Arlington County in Virginia.

Both sides also agreed to impose a media blackout when the talks resume Friday. Only the mediators will be allowed to give status reports on the talks, according to last night's announcement by the FMCC.

As of Monday, the basic disagreements between the company and the union reportedly involved wages, Pepco's proposed changes in job classifications, and proposed sick-leave changes.