The Nuclear Regulatory Commission, in a controversial move, voted yesterday to permit Virginia Electric and Power Co. to begin trial operations of a second nuclear unit at its trouble-plagued North Anna plant.

Vepco officials said the start-up of North Anna 2, which was completed months ago but left idle because of national concern about safety issues, would soon lead to savings for the utility's customers.

"Nuclear power is the safest, least expensive way to generate electricity on the Vepco system," said Vepco executive vice president Jack H. Ferguson. The company predicted it would be allowed to put North Anna 2 into full operation by next August or September, leading to a $2.57 monthly saving for a "typical" customer.

The NRC license, which will allow fueling and low-power testing of North Anna 2, has stirred considerable concern about safety issues.

"We should recognize that this will lead some to conclude that it's business-as-usual and that NRC and the nuclear industry have not learned the lessons of TMI (Three Mile Island)," Edward J. Hanrahan, NRC policy evaluation director, warned the commission in a memo drafted before yesterday's vote.

Nevertheless, Hanrahan said he favored issuing the low-power testing license as a matter of "simple justice." He said that shortcomings at North Anna 2 were the fault of the federal agency, rather than Vepco.

The North Anna 2 license is the second approved by the NRC since the Three Mile Island accident in March 1979. The commission ended a licensing moratorium in February by permitting similar start up operations at the Sequoyah nuclear plant in Tennessee.

The license limits Vepco to testing the North Anna 2 plant at a maximum of 5 percent of its full operating level. To put the unit into commerical service, Vepco must obtain further aproval from the federal agency.

The NRC staff has reported numerous shortcomings in the North Anna 2 unit's control room. Officials note, nevertheless, that the control room is shared by North Anna 1, a Vepco generating unit that has been in operation since 1978.

"We believe that many of the deficiencies identified could cause the operator to take erroneous actions under stressful conditions," the NRC staff said in a report to the commission. "These actions could initiate a transient (a mechanical malfunction or other error) or could exacerbate his response to an abnormal event already under way."

The report cited potential difficulties in reading meters, communications problems because of noise, indicator lamps that cannot be checked to make certain they have not blown out, and other shortcomings. Many of these failings must be corrected by Vepco before North Anna 2 begins commercial service, NRC officials said yesterday.

In urging the NRC to license North Anna 2, however, some officials have complained that any delay was unwarranted because of the unit's similarity to North Anna 1. "There have been no significant events in the operations of North Anna 1 that would reflect adversely on the potential for safe and productive operations at North Anna 2," Virginia Gov. John N. Dalton said in a letter to the commission in November.

Vepco officials have repeatedly pressed for increased reliance on nuclear power, arguing that it is cheaper than oil and coal. Only one of Vepco's nuclear plants, North Anna 1 is currently in operation. Surry units 1 and 2 have been shut down since last year for repairs and tests, a delay that has led to higher electricity bills for Vepco customers.

After the NRC decision was announced yesterday, an aide to the governor said, "You can safely assume that he's delighted."

Amid the continuing controversy, the North Anna plant has been the subject of frequent criticism. In addition, Vepco has been among the most heavily fined operators of nuclear plants in the United States, incurring NRC penalties of more than $100,000.

A discharge of radioactive xenon gas from North Anna 1 last September led to NRC criticism of Vepco. The North Anna plant has also been troubled by a belatedly discovered earthquake fault, soil settlement under its pumphouse, improper turbine placement and several other incidents.