The Virginia Electric and Power Co. had discovered a second possible safety problem at its North Anna nuclear power plant without reporting it until after a license for the plant had been authorized, the Nuclear Regulatory Commission staff said yesterday.

The NRC staff said the double occurrence "raises questions regarding Vepco's commitment" to safe operation of the plant, which is in Louisa County 75 miles southwest of Washington. As a result, the NRC's Atomic safety and Licensing Board scheduled new public hearings for Dec. 29.

Vepco senior vice president William L. Proffitt said the company "followed established procedures" in evaluating both potential problems and reported them to the NRC as soon as it was convinced they were problems.

The NRC asked Friday for the hearings to be reopened upon learning that Vepco had known about a computer coding problem affecting the piping on Dec. 1 but had not reported it until Dec. 15, two days after Vepco won authorization for an operating license.

The NRC yesterday filed a supplemental request for additional hearings, adding its discovery that a problem with printed electrical circuit components had been revealed to Vepco on Dec. 9 but was not reported to the NRC until Dec. 16.

"The staff believes that the timing of the communication by Vepco of this second potential safety problem also raises questions regarding Vepco's commitment and/or technical qualifications to operate" the plant safely, the NRC memo said.

The NRC's Atomic Safety and Licensing Board, which issued the permit authorization, conferred with parties in the dispute by a conference telephone call last Friday, largly to decide whether the reopended hearings should be oral or by written affidavit.

"We argued for public hearings because you can't cross-examine a written affidavit," said June Allen, head of the North Anna Environmental Coalition that has been fighting the power plant for the last five years. She said the coalition was gratified at the decision to take new testimony in the case, adding the group had asked for just such a move four times since the June 2 ending of earlier hearings.

Issuance of the operating license has been held up pending the outcome of the Dec. 29 hearings, which will be held at 10 a.m. in the NRC hearing room in East-West Towers, 4350 East-West Highway, Bethesda.

The first possible safety problem concerned an error in the computer codes used to evaluate pipes and connections in the reactor backup and safety systems. Vepco's Proffitt said the codings had been re-evaluated and found to have no effect on the satety of the system.

The second difficulty revealed yesterday concerned electrical circuit chips, parts of electrical circuit boards that Wastinghouse Corp. supplied. Westinghouse notified Vepco Dec. 9 that some of the chips in the plant control panels might have been constructed so that a vibration could cause them to short-circuit, a Vepco spokesman said.

"The company followed procedures established for evaluation of a potential problem . . . The review was completed on Dec. 16 and the matter reported to the NRC the same day," Proffitt said in his statement. He added that nine circuit cards containing potential problems had been located and replaced on North Anna Unit I, while three on Unit II would be replaced before nuclear fuel is loaded into its reactor.

Unit I was loaded earlier this month as part of the preparations for going into commercial operation, which was then expected to occur in February. Unit II is expected to become operational in another year. The two plants together will add 934,000 kilowatts to Vepco's electrical generating capacity.

Sen. Gary Hart (D-Colo.), whose nuclear regulation subcommittee has jurisdiction over the NRC, last night asked the NRC for a full report on the recent developments. His committee held hearings in October on allegations that Vepco and the NRC had together known about the existence of a geological fault under the North Anna site for three months before it was revealed to the public. Faults are common sites of earthquakes.