The Potomac Electric Power Co. has asked Maryland regulators to speed up the licensing process for a new coal-gasification plant in case the utility needs extra generating capacity before the mid-1990s.

Pepco said it had noticed an unusually high peak demand last June and needed one more summer to determine whether the abnormally high peak was part of a rapidly growing need for electricity or just a glitch. "In June 1984, we hit a peak that was off scale by the order of 250-megawatts. . . . It was extraordinary," said Peter Benziger, senior vice president for generation. "The suspicion is the load growth is real, but we need another summer to confirm" the higher demand.

Should it signal a pattern, Pepco officials say their energy plan -- which includes extending the life of older plants and energy management programs -- could call for building the new coal-gasification plant sooner than anticipated.

The plant, to be built on a 1,000-acre site in Dickerson, Md., is now scheduled to be operating by 1995. Coal-gasification technology converts coal to gas, which is then used to power combustion turbines hooked up to electric generators. Large amounts of waste heat from the process can be used to make steam to drive steam-turbine generators.

The plant could be built more quickly than conventional plants and capacity could be added as needed, Pepco officials said. The plant would be roughly comparable in price to a similarly sized conventional coal-fired unit and less costly to run.

Because the company has asked regulators to streamline the plant licensing, the 360-megawatt plant could be on line by 1991, said Benziger. Licensing the plant requires a Maryland certificate of convenience and necessity and environmental clearances from various state agencies, including the departments of Natural Resources and Health and Mental Hygiene and the Maryland Public Service Commission; this will lead to extensive public hearings, he said.

The plant is estimated to cost $600 million in 1985 dollars, said Nancy Moses, a spokeswoman for the utility. No estimates of the effect on consumer rates currently are available, she said.

The new coal-gasification technology is unproven and costly, say consumer advocates and energy experts. They said that other options, such as long-term contracts to purchase power or the use of cogeneration plants, could alleviate the problem in a more efficient and less costly way.

The outside experts and Pepco are divided about the true rate of growth in electricity demand.

Pepco estimates demand is growing by about 1 to 2 percent a year and that it has a comfortable 20 percent margin of reserve capacity over its all-time peak of 4,490 megawatts last summer. But Bruce Oliver, a consultant to the 1,000-member Apartment and Office Building Association of Metropolitan Washington, claims Pepco's projections are too low and that the plant will be needed sooner than Pepco estimates.

Oliver said Pepco should enter long-term excess-power purchasing agreements with other utilities before demand causes prices to rise sharply. "Then all these proposals for controlling residential air conditioners . . . become unnecessary, and it gives time to look into this coal-gasification technology a little further before they commit to it."