Higher electricity bills are, the biggest threat to Washington area utility customers as a result of the 72-day-old nationwide coal miner's strike, local electric company representatives said yesterday.

Spokespersons for Pepco, Vepco and the Baltimore Gas and Electric Co., said their companies are all capable of converting their plants from coal to oil to prevent electrical shortages. But the switch would raise the cost of electricity in the area because oil is more expensive than coal.

Pepco, which currently relies on coal to power 80 percent of its plants, is the most coal-dependent utility in the area. But according to Gayle Butler, a spokeswoman for the company, Pepco is capable of switching its generators from using coal to using oil within a week.

Butler said Pepco will convert to oil only if its stockpile of coal drops below a 45-day supply.

All three of the utilities estimate that they have about a two-month supply of coal in stock now.

A spokesman for Vepco said the company is not severely threatened because only 36 percent of its generating capacity is powered by coal. The remainder of the company's generators are powered by oil (38 percent) and nuclear energy (25 percent).

Vepco could also convert its plants to oil use within a week, the spokesman said.

The Baltimore Gas and Electric Co. is not being affected by the strike because only a single unit of one of its power plants is fueled by coal, according to spokesman Charles J. Franklin.

Although the metropolitan area is not expected to be affected by electrical shortages, smaller utilities serving communites near Washington may be, since their plants are not as modern and cannot as easily be converted from coal to other fuels.

As a result, two of the smaller utilities near Washington, Potomac Edison and Appalachian Power Co. are being "critically affected," according to spokesmen.

Potomac Edison, which has only 27 days of coal remaining, has requested mandatory restrictions on electrical use in the communities it serves in Maryland, West Virginia and Virginia. Only one state, West Virginia, has given Potomac Edison approval for the curtailment program, which includes rationing electricity.

Potomac Edison serves small communities such as Frederick and Hagerstown in Maryland, Martinsburg in West Virgina and Winchester and Fort Royal in Virginia.

"The strike is affecting us critically," said Lynn Keller, a spokesman for Potoac Edison. "We cannot convert to oil. Well, we could but it would be a lengthy and expensive project."

The Appalachian Power Co., whose coal stockpile has dropped to a 47-day supply, is also being affected by the coal strike.

The Associated Press reported that in a letter to about 1,500 of its customers, the utility warned that future energy conservation measures "will have an increasing effect on our customers and will also lead to industrial cut backs that will result in unemployment."

Appalachian Power serves customers in several areas of Virginia including Roanoke, Lynchburg, Huntington and Charlestown.