Executives of electric utilities that serve the Middle Atlantic states expressed concern yesterday that developing regulatory and energy problems could create power shortages this summer.

This sober assessment, which differs from optimistic forecasts last spring, was delivered to officials from state regulatory agencies at a meeting yesterday near Valley Forge, Pa.

Utilities involved in the new forecast of "areas of concern for the 1979 summer peak season," are members of the Pennsylvania-New Jersey-Maryland [PJM] power pool, which links together into a single electrical system the generating capacity of electric firms in those states plus Delaware and the District of Columbia.

PJM members include Potomac Electric Power Co., which serves D.C. and the populous Maryland suburbs, as well as Baltimore Gas & Electric Co.

Some PJM members are having trouble finding needed oil for their plants and some face shutdowns of coal-burning plants, under U.S. regulations.

Harrisburg-based Metropolitan Edison Co., owner of the crippled Three Mile Island nuclear plant in the Susquehanna River, is a member of the PJM regional power pool. Immediately after the nuclear crisis in central Pennsylvania, PJM officials reviewed the summer outlook and told state agencies there would be adequate reserves even if both units at Three Mile Island remained shut.

Yesterday, however, spokesmen for the region's utilities cited some men developments that now raise concern "for the adequacy of power supply during the latter part of this summer."

Because of the potential problems revealed yesterday, the region's electric utilities said they are canceling immediately all planned maintenance of generating capactiy. In addition, they revealed, emergency procedures for curtailing some service in the event of shortages are being reviewed and updated.

Virginia Electric & Power Co., which faces electrical generating problems of its own because of reduced nuclear plant output, is not part of the PJM pool. However, the power grids to the south [including v. epco] and west of PJM are expected to have less reserve power than the pool for the Middle Atlantic states in the event of a prolonged heat spell or unusual demand.

Edward Mitchell, senior vice president for systems engineering and operations at Pepco, emphasized in an interview that the revised availability forecast should be seen only as a warning of what could happen in a "worst-case scenario."

There are four potential problems faced by the region's utilities and any one of those contingencies could be handled with adequate reserve generating capacity. "But if two occur at once, we're in trouble," Mitchell added.

Before the Three Mile Island accident, PJM was headed into the summer of 1979 with a reserve generating capacity of 35 percent -- the amount of electrical output possible over and above expected of peak demand.

But the Three Mile Island crisis immediately cut reserves to 30 percent. And now, several other developments have threatned to cut the reserve power to 20 percent or less. That provides a relatively small margin of capacity to put into service in the event of unexpected shutdowns at key generating stations.

"At this time we still believe the reserves to be adequate, and the situation manageable," the utilities told state regulators yesterday in discussing four major problems. "However, the uncertainity associated with each concern and the potential impact of the combined effect if the worse case should develop should be noted."

Specifically, the utility executives warned off:

The possibility of having to shut down or reduce some 1,000 megawatts of coal-fired generating capacity because of non-compliance with strict interpretation and enforcement by the Environmental Protection Agency of the Clean Air Act, as of Aug. 7. Currently, EPA has not made clear to the companies what units may be involved but the utility officers said they could not operate plants found to be in violation because of criminal penalties attached.

Continued shutdowns of two nuclear units in addition to the Three Mile Island plants. Delays in repairs have forced plants in New Jersey and at Calvert Cliffs, in Maryland, to be shut longer than anticipated. The two plants produce about 1,900 megawatts and with major repairs now in progress, "there is a possibility that they will not be fully 'shaken-down' for full operation" until several weeks after scheduled return to service on Aug. 8 and July 16, respectively.

At least two PJM comapines are having trouble buying light [distillate] oil required to start generating plants and to provide supplemental fuel at some coal plants. As much as 1,500 megawatts of power may not be available for periods of peak demand because of oil shortages.

An extended heat wave could increase the PJM load above the forecast peak. In addition to nuclear plants now shut [which produce 3,545 megawatts], additional capacity could be forced out of service "for many unpredictable reasons."