Virginia Electric and Power Co. officials for the first time put a price tag yesterday on the cost of the Three Mile Island accident to their customers -- at least $300 million, an average of $230 for each of the company's 1.3 million customers.

"Except for Met Ed (Metropolitan Edison Co., owner of the TMI plant), our company was hurt more by Three Mile Island than any other," said Vepco Chairman T. Justin Moore jr. in an interview.

Officials said the government's reaction to the accident contributed to the shutdown during most of last year of Vepco's massive nuclear units and the refusal of federal regulators to license a fourth. That fourth unit -- North Anna Two, 80 miles southwest of Washington -- has been completed but kept inactive for a year while the Nuclear Regulatory Commission has debated making modifications to nuclear plants based on the lessons of Three Mile Island.

According to Vepco, each month one of its nuclear units is shut down, customers must pay an additional $15 million, most of it for replacement electricity generated in less efficient coal-and oil-fired power plants. Thus the cost for the delay of North Anna Two alone amounts to $180 million in the past year, the company said.

Moore and Vepco President William Berry said customers can expect the final price tag to be even higher as the commission orders new -- and costly -- safety changes. They said modifications so far have ranged from repainting emergency control rooms to adding more safety personnel. Also, new control room operators are undergoing more rigorous training in preparation for the opening of North Anna Two, which officials hope will be running at full power by the end of the summer.

Metropolitan Edison officials have estimated the cost of cleaning up and repairing their damaged nuclear reactor just south of Harrisburg, Pa. at least $400 million. The company is also spending $25 million a month to buy replacement power -- a total of $375 million in the 15 months since the accident.

Nationwide, the electric utility industry has estimated that the accident will cost in the billions, although no one has offered a definitive figure. Carl Goldstein, spokesman for the Atomic Industrial Forum, said most of the nation's 74 completed nuclear units must be outfitted with $30 million in safety modifications ordered by the NRC. But he added that figure did not include the cost of buying replacement power during shutdowns or the cost of new nuclear "shutdown insurance" being purchased by companies.

"We're a long, long way from a final price tag," said Goldstein.

While defending Vepco's heavy reliance or nuclear power, Moore conceded the energy source had fallen short of early expectations. "In all candor, I think that nuclear power was oversold a little bit to everybody," said Moore, who in the past has been one of the country's most ardent nuclear advocates.

In a luncheon meeting with reporters and editors at The Washington Post, Moore cited claims by early enthusiasts in the 1950s that nuclear-generated electricity would prove "too cheap to meter" as one example.

"It (nuclear power) was oversold by the military to industry," said Moore. "The reactor makers like Westinghouse and General Electric oversold it to us to a certain extent . . . And utility executives myself included, oversold it to the public . . .

"We made constant reference to the fact that nobody's ever been hurt or injured or killed (in a nuclear plant accident) . . . Coupled with that statement was the implied warranty that nothing ever could happen. And that was the bubble that Three Mile Island burst."

Moore said the accident had a particularly devastating impact on Vepco because the company had expected nuclear power to carry a large part of its generating load. In 1978, the year before the accident, nuclear power accounted for 35 percent of Vepco's electricity, and at one point, Moore said, the company's three operating nuclear units were producing more than 50 percent.

But the government's reaction to Three Mile Island, coupled with shutdowns of the company's Surry nuclear units for earthquake-hazard repairs and replacement of one unit's massive steam generator system, sliced its nuclear power's 1979 contribution virtually in half -- 17.4 percent for the year, company officials said yesterday.

"These nuclear plants have been down a hell of a lot for reasons that I don't think Vepco could have foreseen or controlled," said Jack Ferguson, Vepco executive vice president in charge of power.

Company executives yesterday again rejected charges from consumer advocates that the utility's mismanagement was a major factor in both the company's nuclear power and financial troubles. Moore and Berry outlined what they described as a major reorganization of the company's management, which included the hiring last February of Ferguson, a longtime nuclear expert and one of the few top Vepco executives who did not rise through the company's ranks to his present position.