The shutdown of the Virginia Electric and Power Company's Surry nuclear generating plant may lead to a power shortage this summer and will be more costly than previously estimated, company officials said yesterday.

The utility's two Surry units in southern Virginia were among five nuclear plants ordered closed Tuesday by the Nuclear Regulatory Commission. The agency decided that a computer formula error might have made some of the plant's cooling pipes too weak to withstand an earthquake.

NRC officials said it would take "some months" for the problem to be evaluated at each plant and for any needed repairs to be made. But Vepco executive manager E. Ashby Baum told a congressional committee yesterday that a closing of more than one month would mean the company's conventional plants would have to run overtime, past their regular maintenance periods, to make up the lost electricity.

"We thereby run the risk that those plants will not be available to meet the (heavy) summer demand and that we may have to curtail service to our customers," Baum said.

Vepco officials have noted that the company's nuclear plants currently produce 36 per cent of the company's power and that during periods of peak summer demand the company may not be able to purchase adequate supplies of power from other electric companies.

Baum also revised upward yesterday the company estimate of what Vepco's 1.3 million customers -- many of them in Northern Virginia -- will have to pay because of the Surry shutdown.

Buying oil to fire the conventional plants to make up for Surry, he said, will cost $375,000 per day, or $12 million per month, "and the figure would be twice as great except that Surry II (one of the two units there) was already shut down." The plant is closed for replacement of its clogged steam generating system.

Earlier Vepco had placed the cost of the closure at $275,000 a day, or an increase of about 6 per cent in the typical residential bill. The revised figures given congress yesterday indicate that the typical Vepco customer would see about an 8 per cent increase in his electric bill, or an increase of about $2.75 a month on the average residential bill of $41.

Sen. Gary Hart (D-Colo.), whose subcommittee on nuclear regulation had called Baum to testify, asked why Vepco assumed customers would have to shoulder the additional costs. "I'm concerned that the customer and the ratepayer will get it in the ear," Hart said, "even though the customere didn't make the mistake."

"All added fuel costs are passed on," Baum replied.

He noted that Surry engineers and Vepco officials are convinced the plants are safe to operate and that no prolonged shutdown will be needed. Surry should have been allowed to conduct the review of its piping system design while continuing in operation Baum said.

The plants, he said, are designed to withstand an earthquake of a strength that might occur once in every 12,000 years. "The possibility that such an event would occur in the next three weeks would be extremely small," he said.

Sen. John Warner (R-Va.) asked Nuclear Regulatory Commission Chairman Joseph Hendrie at the hearing whether the commission had ever considered giving Vepco officials the opportunity to argue that the plants remain open during the checks. "It was an option and we did consider it, but we felt it was best that we didn't do it," Hendrie answered.