Virginia Electric & Power Co. and state civil defense officials are preparing for the closest thing to a nuclear disaster since the Three Mile Island incident -- a simulated meltdown at Vepco's North Anna nuclear reactor to test Virginia's ability to protect local residents from atomic accidents.

Early Saturday morning, Vepco officials will discover mock malfunction at the Louisa County plant and sound the alarm for an eight-hour dry-run disaster, culminating in the simulated evacuation of 15,000 people from five counties.

The North Anna emergency war games will involve hundreds of people, from Gov. John Dalton to the Mineral Volunteer Fire Department in the most massive ersatz emergency Virginia has ever seen.

The exercise will be monitored and graded by the Federal Emergency Management Agency, which in a report just issued found most states are poorly prepared for nuclear accidents.

"Clearly it has to be a satisfactory exercise," said Sheldon Schwartz, acting director of FEMA's Radiological Emergency Division.

The Nuclear Regulatory Commission two weeks ago voted to hold up the license for Vepco's North Anna 2 reactor until after this weekend's safety drill, and Schwartz said every nuclear plant now will have to pass the test before it can begin operation.

Vepco and the state Office of Emergency and Energy Services have been preparing for the simulated disaster for months but have disclosed few details of the exercise to keep it as authentic as possible. They've scheduled a press conference Friday to alert the news media to their part in the massive maneuvers.

The scenario prepared by FEMA, state officials and Vepco calls for the test to begin shortly before 7 a.m. Saturday in much the same way the Three Mile Island incident did -- with a chain reaction of mechanical malfunctions that gets worse and worse, giving players in the game the opportunity to respond to an escalating emergency.

The governor will take charge of the test of the state radiological emergency plan from an underground control center at the State Police Academy in Richmond, then will be flown by a National Guard helicopter to the plant for a press conference, said Michael LaCivita, information director for the Office of Emergency and Energy Services.

The state emergency office is to alert half a dozen other state agencies plus law enforcement officers and volunteers who will be deployed across Louisa, Hanover, Orange, Spotsylvania and Caroline Counties.

As the simulated nuclear accident escalates from an "event" to an "alert" to an "on-site emergency" and finally becomes a "general emergency" when the reactor core starts to melt, an emergency evacuation plan will be put into effect.

Buses will roam the countryside within five-mile radius of the plant following the routes they would take to evacuate residents in a real emergency. State police, local lawmen and volunteer firefighters will all be called in.

Volunteer victims will flee the make-believe radiation. A Vepco helicopter will rush an "injured" worker from the plant to a nearby hospital to see whether medical facilities are able to treat a patient who must be isolated to protect others from the radiation.

"It will be as authentic as we can possibly make it," said Kerwin Fisher, a Vepco press officer, whose duties will be to avoid the public relations disasters of Three Mile Island.

The eight-hour exercise will compress a series of events that might take 64 hours during a real crisis, Fisher explained.

At each stage, FEMA referees will evaluate the way Vepco and state officials respond to each new problem, to see whether they do the right thing.

Neither Vepco nor state officials are willing to estimate how much the exercise will cost, but ultimately the bill for emergency preparations at nuclear plants will be paid by electric customers. Emergency planning is part of the cost of nuclear power, federal officials say, and FEMA has no plans to provide money even for tryouts.

FEMA regulations now under consideration ultimately will require Vepco to install a massive siren sytem -- or some other communications device -- to alert everyone within 5 miles of the nuclear plant within a half hour of a disaster. Vepco says that will cot $3.2 million.