A spokesman for the Virginia Electric and Power Co. incorrectly informed The Washington Post that the rate for its customers averages about 2 cents a kilowatt hour. The correct figure is about 4 cents a kilowatt hour.

Virginia Electric and Power Co. overcharged about 600 Northern Virginia residents on electric bills sent out over the last three weeks, the company said yesterday.

The overcharges occurred on bills sent to Alexandria, Fairfax County and Woodbridge customers, company officials said, but the amounts of the overcharges were unknown yesterday. One Hollin Hills resident with an all-electric home was overcharged at least $30.

The overbilling occurred in the fuel adjustment charges that since 1972 have been tacked onto the electric bills of Vepco's million customers. The fuel adjustment charge passes onto consumers increasing - or decreasing - costs of fuel to run Vepco's generators. It varies from month to month.

Customers will be credited with the overcharge in their next bills, but company officials said yesterday they did not know whether customers would be otherwise notified that they had been overcharged.

The overcharges were brought to Vepco's attention last week by at least one irate Fairfax resident . John Joyce, a government economist, said he called local Vepco officials when his January electric bill arrived late. He discovered he had been billed a February fuel adjustment charge for the month of January. The February rate was almost four times that of January. This was because Vepco earlier had shut down its Surry nuclear power plant for repairs and recharging and had to buy expensive power from other power companies.

Under State Corporation Commission regulations, if a customer is billed on Feb. 1 for the preceding 30 day period, Vepco charges him the February fuel adjustment rate. Joyce and most of the other 600 overcharged customers normally are billed at the end of the month. However, in January their records were being moved from one Vepco office to another and they were billed late, in early February, a Vepco spokesman said.

Vepco is adjusting the 600 customers' accounts, charging them the January fuel adjustment rate.

Joyce, however, believes that the whole billing method is unfair. "It's not fair to those billed on the first of the month, or early in a month, and it would be very easy to change, to charge customers proportionately. All they have to do is change three lines in their computers," Joyce said.

Company officials say the method evens out because when the fuel adjustment charge goes down again, as it is expected to do later this spring, those billed at the beginning of a month will be the first to benefit from it.

The fuel adjustment charge is .00451 cents per kilowatt hour for February compared to January's .00126 cents, and is expected to go even higher in March, a Vepco spokesman said yesterday.

Vepco charges its customers roughly 2 cents a kilowatt hour for electricity - 1.389 cents of it to pay for fuel to fire Vepco's coal, oil and nuclear generators.

Under the fuel adjustment charging system customers are charged extra whenever fuel costs rise above the 1.389 cents per kilowatt hour base and are given credits whenever fuel costs drop below that, Vepco official explained.