Power companies serving the metropolitan Washington area should be able to produce enough electricity this summer to avoid brownouts and other service cutbacks, U.S. and utility officials told a congressional inquiry yesterday.

The Potomac Electric Power Co. and other utilities linked in a power-distribution network north of the Potomac River should have production capacity 21 percent to 24 percent greater than the expected peak need, Pepco senior vice president Edward F. Mitchell told a special House District of Columbia subcommittee.

The situation will be much tighter south of the Potomac, where three nuclear plants owned by the Virginia Electric & Power Co. currently are shut down and a new fourth plant is scheduled to begin service in August.

Stanley Ragone, Vepco president, said his Richmond-based firm will be squeezed to 1.9 percent reserve capacity in June. By August, with three nuclear plants expected to be in service, the margin should rise to 15 percent, he said.

If all the nuclear plants are not put into operation. Vepco's power-generating capacity will fall below the need of customers in July, according to figures he submitted.

Ragone insisted that Vepco will be able to buy enough power from utilities in adjacent areas, notably from the American Electric Power System that serves the Appalachian area and has excess production in the summer.

Pressed by Rep. Herbert E. Harris (D-Va.) who suggested that Vepco should make firm arrangements now to buy such power, Ragone said such a move would be costly.

"I am not going to sign an agreement today . . . that I'm going to buy any amount of power in July or August," Ragone said, "because if I do, I have to pay for it" whether it is used or not.

Jerry L. Pfeffer, an acting assistant administrator of the U.S. Department of Energy's Economic Regulatory Administration, said power-sharing arrangements among Power companies were "something like an old-boy network," but they generally work.

Pfeffer affirmed the estimates made by Pepco and Vepco, and said "there are ample reserves available," from Vepco's neighbors to serve Virginia. If a crunch were to occur, Pfeffer stressed, his agency would not hestitate to use its legal authority to order power diverted into the state.

Ragone's estimate of Vepco's power-generating capacity was more optimistic than testimony by another company official to a Senate subcommittee on March 26. The official said an extended shutdown of Vepco's Surry nuclear plant could lead to power curtailments to customers. Ragone was not questioned on this point yesterday.