A story in the Jan. 31 Business & Finance section paraphrased Potomac Electric Power Co. chairman W. Reid Thompson ina way that suggested that reliance on coal and programs to hold down operating and construction costs had contributed to rising prices. Thompson cited those factors as aids in holding down rising prices.

The District of Columbia Public Service Commission has ordered a change in residential customer charges by WashingtonGas Light Co. that will increase bills by approximately 3 percent.

The PSC, which granted a rate increase of $11.9 million to Washington Gas last October, decided earlier this week on how to allocate the charges to make up that increase.

The change will mean an estimated increase of 20 cents a month on the average residential heating customer's bill of $60.70. For the average bill that doesn't include heatingcosts, the increase will amount to about 24 cents a month added to the average cost of $7.14.

In effect, what the change does is allocate charges so that heavier users pay somewhat lower rates, a WGL spokesman said. The order, signed on Jan. 21, took effect last Monday.

In another action, Potomac Electric Power Co. yesterday asked the Maryland PublicService Commission for authority to increase rates 4.3 percent, or $18 million. The company said the request reflectedhigher costs since November 1979, the end of the year on which Pepco's present Maryland rates are based.

Pepco President W. Reid Thompson said that much of that increase was because of reliance on coal for fuel and programs to hold downoperating and construction costs.

The proposed rate increase would add nearly 7 cents a day to the bill of an average residential customer in Maryland, the company said.

On Thursday the Maryland Public Service Commission granted Chesapeake and Potomac Telephone Co. of Maryland a rate increase, which went into effect yesterday, allowing the company $25.3 million in additional revenues each year. It was considerably short of the 10.4 percent increase for which C&P applied last July.

"We are shocked and perplexed by the decision," said C&P Vice President J. Henry Butta. "The commission obviously disregarded hundreds of pages of testimony whichclearly justified the need for a revenue increase of over $90 million."