The Three Mile Island nuclear power plant accident that shocked this area and the nation almost a year ago has been a good thing for at least one group: organized labor.

While the plant's owners have teetered on the edge of bankruptcy, its customers have faced sharply higher rates and its neighbors have agonized over possible health effects, consider this:

The number of on-site workers at the TMI plant, located on a Susquehanna River island across from this tiny central Pennsylvania town, has risen from 560 at the time of the accident last March 28 to 1,700 now.

The on-site employment figure is expected to peak at about 3,000 when decontamination and cleanup work, expected to take three to four years, begins in earnest.

At a time when the nation's building and trades unions are losing substantial ground to nonunion contractors, General Public Utilities Corp., TMI owner, has decided to give organized labor a major boost.

GPU will sign Monday a multimillion-dollar "no-strike, no-lockout, no-slowdown" contract with 15 building and trades unions and the Internation Brotherhood of Teamsters, all of whichwill share significant parts of the TMI recovery work.

The signing of the "TMI Recovery Project Agreement" will take place at a Harrisburg hotel several miles northwest of here and will be attended by Labor Secretary Ray Marshall, among others. The event is being hailed by some of its promoters as "a new beginning in labor-management relations, a unique opportunity for us to work together in the public interest."

While many here and in surrounding areas disagree that restarting the critically damaged TMI plant is in the best interest of the public, few contest the belief that failure to revive the facility could be fatal to the nuclear industry.

Both labor and management representatives acknowledge that that is the main reason for their contract and for the estimated $400 million to be spent on recovery.

"We know that the situation in this area is that a lot of people don't like the idea of starting up the plant, but somebody's got to put this. . . thing back into operation," said a spokesman for the AFL-CIO Building and Trades Council.

"I'm not saying this just because ourpeople are going to get jobs. We need this plant. It has long been our policy that coal and nuclear energy are the only workable alternatives to help our nation meet its immediate energy needs.

He added: "We're not callous to concerns about public safety. We're as concerned about safety as anyone else. After all, it's our people who are going to be working in there."

The cleanup job is a gargantuan, dangerous undertaking requiring a varity of technical, construction and maintenance skills. Hands are needed to build the large, concrete vaults, now beginning todot the plant's grounds, for the burial of radioactive mateial.

Specially equipped trucks, presumablyto be driven by Teamstes, will be needed to cart away tons of solid radioactive material if the Nuclear Regulatory Commission approves disposal plans now under consideration by TMI officials.

Dealing with the partly melted nuclear fuel core inside TMI's Unit 2 containment building, the site of last year's accident, is regarded as an especially ticklish operation.

The recovery agreement allows the company to use its own experts and specially trained employes to work on such projects as removing and replacing the damaged core. But many other workers will be needed to clean residual radiation from the containment building walls.

The cleanup work has been delayed by about four months because of equipment failures and strong public opposition to some proposals such as the venting of radioactive krypton gas inside the damaged structure.

Some GPU officials say they have to remove the gas in the containment area before any significant work can begin.

"Right now, we can put some people inthere in 90-pound protection suits. But they wouldn't be able to move around much, or do much, or stay in there very long," said TMI spokesman David J. Delzingar.

He said immediate maintenance is needed on air pressure equipment inside the containment building. The failure of that equipment, which has been operating continuously since the accident, could lead to the uncontrolled release of krypton gas, Delzingaro said.

At least 12 GPU employes have volunteered to go to work in the containment building when the gas is purged, the TMI spokesman said.

"They said they wanted to be first togo in there," said Delzingaro. "It's something of a pride thing. . ."

The "pride thing" is reflected in interviews with past and present TMI workers, most of whom would talk to reporters for background only.

"Look at this," said a construction worker helping to put together the Epicor II water infiltration apparatus that TMI officials hope will help clean up about 600,000 gallons of radioactive water covering the floor of the containment building.

"I'm pretty proud of the work we're putting into this system because it's being done right, exact, and that requires a lot of skill. I can't tell you who screwed up this Unit 2, but this baby is going to work," he said, patting the outside wall of the blue Epicor structure.

At least eight employes have sufferedradiation overexposure at the plant since recovery efforts began; two otherswere exposed at the time of the accident. But GPU officials contendthat none of the workes was seriously injured.

TMI workers know about the overexposures, but none of those interviewed seemed disturbed by the prospect that the same thing could happen to them.

"If you're working with something, you can't be afraid of it," said an electrician who worked on the TMI Unit 1 generator, which has been shut down since the accident and is being partly remodeled.

Spokesmen for the International Brotherhood of Electrical Workers, which represents utility workers and a share of the construction workers not at TMI, expressed a similar attitude.

"Last year, we lost 72 electricians, most of them linemen," said IBEW public relations director Robert W. McAlwee.

"That proves that electricity in and of itself can be dangerous, but most people still park their cars under power lines," he said.

Nuclear opponents here say the TMIworker's good salary (about $11.36 an hour for the average IBEW worker, for example) is the chief reason for loyalty to the company and the nuclear industry.

"They're trading their future health for a pay check," said the sister-in-law of one worker at a hearingon the krypton venting proposal last week.

Comments like hers illustrate a schism in the town -- one of the main reasons the workers prefer anonynity.

"The people here are still very emotional over this situation," said Middletown Mayor Robert Reid. "We have a lot of people here who don't want the plant. We have others who make their living from it.

"They're in two separate camps. It's really divided our little town."