For the first time in a decade, the Virginia Electric and Power Co. today asked the State Corporation Commission to reduce customers' bills by an average of 4 percent because of lower than anticipated fuel costs.

If approved, the decrease would mean a $2.75 reduction in the monthly bills of homeowners using an average of 1,000 kilowat hours of electricity. At the same time, however, officials for the Richmond-based utility said they still intend to seek a 5 percent rate increase that they requested in March.

"The rates are complicated, but with a fuel adjustment decrease and a rate increase, the final bill the average customer pays won't be any less," said Randy Phillips, research director for the Virginia Consumers Congress, which in the past has accused the company of financial mismanagement.

Nonetheless, Vepco's projected decrease in fuel costs came as a surprise. The company has always asked for more money at quarterly fuel hearings held by the state commission, which regulates the company's rates.

"We'd have to go back to the '60s to find something like this [decrease]," said Bernard Henderson Jr., assistant to the SCC commissioners, adding, "It's about time."

Vepco Executive Vice President William W. Berry said the company was scaling down its projected fuel costs for the remainder of 1980 in part because the cost of oil had not gone up as fast as company analysts had originally predicted. Vepco generates about 21 percent of its electricity at oil-fired plants.

Berry also cited as factors a decrease in the amount of electricity used this year by residential and commercial customers and the fact that the company has been able to purchase power from other utilities at rates cheaper than if the company produced its own oil-fired electricity.

Vepco expects to buy 13 percent of its power from neighboring utilities this year.

Berry noted that an important element in Vepco's ability to keep fuel costs down will be the successful operation of the company's four nuclear plants. The plants have been troubled in the past by mechanical breakdowns, operator errors by Vepco employes and federal regulatory delays. At present only two of the four plants are in operation.

The company says it expects to have all four of the nuclear plants, whose fuel costs are considerably below these of oil and coal-fired plants, running by the end of summer -- a projection that some critics believe overly optimistic.

Vepco's Surry One reactor, located 130 miles southeast of Washington, reopened earlier this month after a shutdown of more than a year for inspection and repair of possible earthquake hazards.

Surry Two underwent the same shutdowns for earthquake hazards and replacement of its costly and elaborate steam-generator system. It is expected to be back on line next month.

North Anna One, located 80 miles southwest of Washington, is working, but North Anna Two, originally due to open last summer, has languished while awaiting approval of the Nuclear Regulatory Commission. The Commission suspended new reactor licenses last year pending final decisions on its analysis of the Three Mile Island accident. Vepco hopes to have the reactor on line by September and expects nuclear plants to supply 29 percent of its power this year.

Berry said today that the unplanned outages had cost customers as much as $80 million last year for replacement fuel and power.

The company predicts it will need $35.5 million less for fuel costs this year than it had originally told state regulators, last December. Based on winter power rates, the decrease would lower monthly bills from $63.27 to $60.52 for an average residential customer.

At the same time, if the company is granted the $77.1 million increase in rates it requested six weeks ago, the typical customer can expect to pay $63.85. The net effect: an increase of 58 cents a month.