The Virginia Electric and Power Co. yesterday warned that its customers will face blackouts and curtailment of service this summer if it is not allowed to operate, by May, one of its nuclear power plants ordered closed this month by the Nuclear Regulatory Commission.

The power company issued the warning after determining that its preliminary evaluation of the problem at the Surry, Va. plant -- originally expected to be completed this week -- will not be finished until May.

The company is asking the NRC for permission to operate the plant on an interim basis after the preliminary analysis is done and before the final analysis is completed several months later.

If the NRC refuses interim service, "Vepco would have inadequate generating capability this summer and curtailments may be required," the company said in a statement released last night.

NRC officials could not be reached for comment last night. A commission spokesman said that NRC and Vepco members met yesterday morning but he was unaware of what transpired.

A source close to the situation, however, said that the May deadline for the analysis was contrary to what the power company had led commission members to believe.

On March 13 five nuclear plants, including two units at Surry, were ordered closed by the NRC when it found the computer codes that designed earthquake resistance of the piping in the cooling system were in error. The NRC expressed fears that the flaws might cause the pipes that carry collant to the nuclear units to rupture during an earthquake.

One of the Surry units, however, already had been shut down before the NRC order because one of its steam generators needed to be replaced.

Vepco has estimated that it will spend $10 million more a month to generate power because of the Surry shutdown. A Vepco spokesman yesterday said if the interim operation is not approved Vepco may not be able to purchase enough replacement power from neighboring utilities to make up for the loss of the Surry plant and that he did not know how much more might be added to the estimated $10 million a month.

Vepco said that its 1.3 million customers would have to pay 8 percent more in their bills to cover the costs of buying oil for conventional plants to generate power during the Surry shutdown.

The computer errors that caused the shutdown were blamed on work done by the Boston engineering firm of Stone and Webster, the same firm that is performing the preliminary analysis of the Surry problem.

The deadline for the preliminary evaluation was altered "ater further assessment of the scope of work required," Spencer said. "We hope this evaluation will demonstrate to the NRC that the plant can safely resume operations on an interim basis pending completion of the more extensive and detailed analysis."

The Vepco spokesman said that the curtailment of service would be similar to that experienced in January 17, 1977 when a nuclear power station was shut down by ice floes and two conventional generating plants froze up.

At that time more than a third of Vepco's 300,000 Northern Virginia customers had their electricity cut off for up to 2 1/2 hours. If curtailment is necessary it would affect customers on a rotating basis.