Negotiators for Potomac Electric Power Co. and Local 1900 of the International Brotherhood of Electrical Workers have reached agreement on most "non-cash items" in extended bargaining for a new contract.

But differences over bread-and-butter issues remained largely unresolved last night as bargainers continued haggling over wages, benefits, job classification and work-rule changes.

"It appears as though we've got a way to go yet--a lot of negotiating to do before we can reach complete agreement," said Charles Scott of the Federal Mediation and Conciliation Service, who has been monitoring the talks.

Scott said last night that the bargainers "were just into the early stages of discussions on economics."

A three-year contract between Pepco and Local 1900, covering 3,500 of the company's 5,400 workers, expired at midnight Monday. Union members yesterday passed out handbills at Pepco plant sites. But IBEW officials steadfastly played down any strike talk, even going so far as to say the handbill distribution should not be regarded as informational picketing.

"The company passed out its rhetoric, and we were just passing out ours. We weren't picketing," one union official said.

Pepco negotiators offered the union "a total contract package" shortly before midnight Monday. The union recessed the bargaining one hour later to study the company proposal. Bargaining resumed at 1:30 p.m. yesterday, recessed at 10:15 p.m. last night and is scheduled to resume at 1:30 p.m. today at the Westpark Hotel in Rosslyn.

Sources close to the negotiations said Local 1900 bargainers planned to make a counterproposal to the Pepco offer last night. Sources for the company and the union declined to give details.

Key elements in the "non-cash items" agreed to include grievance procedures and health and safety measures, as well as relatively routine matters as composition of the union bargaining unit.

Both the company and union say they want to avoid any walkout.