Jane Fonda would not approve. Then again, maybe she would.

It's everything you need to run a nuclear generating plant--hundreds of lights and switches, dozens of colored gauges, a full-color video-display tube or two. Right out of the "China Syndrone." You expect Jack Lemmon to be sitting at the controls, like in the movie, saving the world from nuclear disaster.

Except for one thing: There's no nuclear reactor for miles.

It's all a fake, but a very canny fake--a simulator designed to train the operators of one of the nation's big nuclear plants. On it, an instructor can replicate thousands of situations--leaky valves, cracked pipes, and the like--so operators can learn to avert potential nuclear disasters, as well as to handle the more mundane day-to-day tasks of operating a generating plant.

Tucked away in a warehouse-like building outside Columbia, the simulator is undergoing finishing touches before shipment to the electric utiltity that ordered it from its builder, the Link Simulation Systems division of Singer Co. And there are about a dozen like it scattered around the huge building, in various stages of readiness, earmarked for utilities in the United States, Sweden, India and elsewhere.

They look like huge video games, except that there's no place to put a quarter. And you'd need a lot of quarters--the pricetag on a good generating-plant simulator can be as much as $9 million.

That's about what General Public Utilities agreed last month to pay Singer-Link for a simulator for training operators for the eventual reopening of the ill-fated Three Mile Island nuclear plant.

"Given the problems in the control room and with training we identified as a result of the accident, both we and consultants we hired felt that we should add a simulator to our training program," said a spokesman for General Public Utilities, which has been using a borrowed simulator for training for several years.

Indeed, the notorious 1979 accident at Three Mile Island was a boon for the nuclear-plant simulator business. Most of the 50 that Singer has sold since it began building the devices in 1968 have been built since the Three Mile Island incident--including the 20 now under construction.

"Three Mile Island caused the business to burgeon rather significantly," says Robert J. Aebli, president of Singer's simulation systems division.

Power-plant simulators--Singer also builds them for training operators of fossil-fuel-powered plants--account for about half the business of the Silver Spring-based simulation systems division. The 2,000-employe unit also produces a variety of simulators for use by the military, including devices that simulate antisubmarine warfare and other naval action, and even mobile simulators that can play complicated war games using computer-generated battlefields, troops and equipment.

The simulation-systems business is an outgrowth of Singer's famed Link Trainer business, a Binghamton, N.Y.-based division that makes simulators used for training pilots for everything from Piper Cubs to the Space Shuttle. "Simulation covers a variety of things," says Aebli. "Things with wings and wheels and things that just sit there while dials move."

Singer's nuclear-plant simulators not only are replicas of the plants' control rooms. They also replicate, in great detail, the response to a variety of actions by using 32-bit computers to simulate, with the laws of physics, the results of various pressures, temperatures and other factors on the mock reactor and its plumbing. Says Aebli: "We do not just store results so that every time you hit a switch, this"--he snaps his fingers--"will happen."

That provides just about an endless number of possible responses to the roughly 10,000 problems a power-plant-simulator operator can throw at a trainee. Nobody has to learn that many possible problems; in fact, Singer says it doubts that anybody gets trained on all of the 250 generic problems that spawn those thousands of variations. But the simulator allows a utility to put operators through all sorts of crisis situations without causing an actual nuclear catastrophe. As with flight simulation, power-plant simulation lets a trainee experience everything but an actual crash.

Power-plant simulators, though, lack the carnival-ride-like action of a flight simulator. The only action is in the lights and switches, and because many actions in a nuclear plant take hours to produce results, the simulators also lack the quick response of a flight trainer--even though everything happens in "real time."

It takes Singer about three years to build a power-plant simulator, and each one must be custom-designed--technology changes and individual utility specifications can cause wide differences in the control rooms of power plants built by the same manufacturer to similar designs. A control-room simulator under construction in Singer's Columbia facility for a Swedish utility bears little resemblance to one being built a few feet away for an American plant that's been producing power for several years but is only now getting a simulator.

Singer officials say the simulators serve a function in addition to training operators--they have proven to be good design checks. Because many are built years in advance of the generating plants they represent, some of the simulators have turned up glitches in plant-control design that can be corrected long before the plant is operational. "Essentially what we're doing is putting a great big magnifying glass on the design," Aebli says. "It's like a design review, I guess." While business is booming for Singer's power-plant simulators--the company has built more than the rest of its competitors combined--the nuclear-plant simulator business is facing a meltdown. With no new plants being planned by utiltities, and those already under construction either being made operational or being canceled, Singer is watching the business for its simulators dry up.

To counter that, the firm has started diversifying its commercial simulator business. It has already built simulators that replicate operations at petrochemical refineries, and Singer officials believe they can also adapt the technology to train operators of the robotics-filled factories of the future.

"Obviously, the nuclear market is depleting," Aebli says. "However, there are other areas . . . in which the technical expertise is allowing us to expand."