Virginia Electric & Power Co. has appealed to customers to turn off air conditioners and other "nonessential" electric appliances, after a small electric fire early yesterday forced a shutdown of its only operating nuclear plant.

Vepco was forced to purchase nearly half of the power it needed to meet customers' demands yesterday, and the utility prepared for a rotating blackout, in which power would be cut off briefly to various parts of its service area, one after another.

"We were prepared for a load-shedding process," Vepco Vice President John Oatts told a news conference in Richmond yesterday. "This did not occur and we do not expect it to occur," he added.

The Surry 1 unit on the James River near Richmond went back into service early yesterday evening, Vepco said. The North Anna 1 nuclear power plant in Central Virginia, which has been shut down since May 23, is expected to be back in service today.

However, Vepco renewed its request for volunteer power conservation today.

Vepco already was facing a serious power-supply problem because of the arrival of hot, humid weather this week which sent electricity demand soaring.

On Monday, Vepco was forced to reduce voltage by 5 percent throughout its three-state system.A Vepco spokesman said the voltage reduction wasn't at a "brownout" level that might pose a potential threat of damage to electrical equipment. The reduction wouldn't be noticeable to customers, Vepco said.

Yesterday, as temperatures edged close to the 90-degree mark in Northern Virginia, Richmond and elsewhere in Vepco's service area, the shutdown of the Surry 1 nuclear power station made the situation "more critical," Vepco said.

"Electric supplies are limited, and Vepco needs its customers to conserve as much as possible to prevent a more serious problem," the company said in a statement yesterday morning.

The request applied to residential, commercial and industrial customers in the parts of Virginia, West Virginia and North Carolina served by Vepco. Maryland and the District of Columbia aren't served by Vepco.

The fire that caused the shutdown of the Surry 1 plant occurred just after midnight when a small transformer unit failed, overheated and burst, spraying oil on electric wiring which ignited. The fire was spotted by an employe and extinguished without difficulty, according to James Burke, resident inspector for the Nuclear Regulatory Commissioner.

However, the fire caused short circuits in a large cable unit supplying power to the control room, causing the reactor to shut down automatically.

When the power loss affected some of the safety instrumentation in the control room, the reactor's emergency cooling system was automatically activated briefly, Burke said. Removal of the cooling water delayed the reactor's return to operation yesterday, he said.

Vepco reported a "small release" of radioactive xenon gas from the reactor building at 8 a.m. yesterday, calling it a normal step in restoring the unit to full power. Twenty employes were removed from the plant as a precautionary measure, but the discharge was a small fraction of the safety limits set by the NRC, Vepco said.

The release wasn't detectable by monitoring equipment outside the plant, Vepco said.

The Surry plant was the only one of Vepco's three nuclear units in service Monday. It's shutdown meant that 10 percent of Vepco's 64 nuclear, hydro-and fossil-fuel-fired generating plants were out of service for various reasons. Together, they account for more than half of Vepco's 9,999-megawatt capacity.

The North Anna 1 plant has been shut down sevral times this year, including one in February when a workman's shirt caught on the handle of a circuit breaker, cutting off power to the reactor control rods and causing an automatic shutdown.

The peak power demand in the Vepco system yesterday reached about 6,300 megawatts, a company spokesman said, and the company had to purchase 2,880 megawatts to meet the demand.

Voluntary conservation by customers saved several hundred megawatts, company officials estimated.

The return of North Anna 1 and Surry 1 to service will add nearly 1,700 megawatts of generating capacity, Vepco said.