At the stroke of midnight on a holiday weekend, without warning, the unionized guard force walks off the job across on entire state prison system. Loaded weapons are left in the guard towers of this maximum-security prison. At a facility for juvenile delinquents, residents are awakened by guards who throw keys on the floor and tell them they're on their own.

The prescription ought to be one for disaster - and indeed, the guard force, organized by the Wisconsin State Employees Union - had every reason to believe that some institutions, particularly the Waupun prison, with its history of attacks on guards, the taking of hostages, and clandestinely held weapons, would "blow" in ugly violence.

But the potential holocaust failed to materialize - thanks to careful planning by prison officials and, more particularly, the prompt intervention of the Wisconsin National Guard.

Now, three months after the strike, it's clear that the illegal work stoppage triggered not just a proud moment in National Guard history, but a small revolution in penology as well.

During the 15-day period that the National Guard substituted for the professional guards, there were scarcely any incidents - far fewer than in any normal period. The habitual harassment of inmates, practiced by a few of the regular guards, stopped instantly.

Inmates at Waupun now tell a visitor that the guardsmen, by "treating us as men rather than animals," won their universal admiration. They even made the guardsmen "honorary screws" (prison slang for guards) and staged, through the prison chapter of the Jaycees, a banquet in the Guard's honor. One inmate said it was "wonderful to be in the care of custodians who relieved me of the illusion that I was nothing but a captive, garbage and a [WORD ILLEGIBLE] to our state and country."

But Wisconsin's "happy ending" - in such stark contrast to the bloody histories of Guard intervention at Attica State Prison and Kent State University - was no accident. The Wisconsin Guard has a highly professional, humanitarian commander in Lt. Gen. Hugh Simonson, selected by former Gov. Patrick Lucey (now U.S. Ambassador to Mexico). Lucey and his successor, Martin Schreiber, refrained from provocative remarks like those attributed to Ohio Gov. James Rhodes preceding the tragedy at Kent State.

Guard preparedness was a first key to the Wisconsin success. "We didn't just walk into the institutions," Simonson explains. "We had operational plans all laid out; everything was rehearsed." For three years , specific Guard units had been assigned to all the prisons in the event of disturbances or work stoppages. Exact rules of engagement had been announced, including strict limits on carrying weapons.

Equally important was the approach Simonson spelled out to his units. "I know nothing of the penal system or psychiatry," he says. "But I do know the residents are human beings. They come out of the society: the justice system says they have erred and must serve a set period of time. It's not our mission to impose any more punishment."

The guardsmen, Simonson says, "didn't baby or mollycoddle the residents. No, we treated them like men."

No general lock-up was ordered. It wasn't the inmates' fault, Simonson notes, that their guards were on strike. The Guard refused to enforce petty rules. Military file was no longer required of prisoners marching to and from recreation or meals; voluntary seating was instituted in the cafeteria and movies; dress codes were relaxed. The men were allowed, for the first time in living memory, to talk along the cell ranges and after lights out and to pass cigarettes and newspapers between cells.

It took the outside intervention to make it clear, says state corrections administrator Allyn Sielaff, that "many of those old rules served no useful purpose." So the returning regular guards were told to enforce them no longer.

Sielaff notes one important caveat to the National Guard's positive experience: that the guardsmen were in the prisons for only a limited period of time. "There's a natural honeymoon," and no one can say "what would happen if the Guard were there for the long haul, as our people are," he says. Some 40 guardsmen have, in fact, applied for permanent prison-guard positions.

Waupun inmates Joe Davis and Jim Anderson - serving terms for armed robbery and domestic homicide respectively - told me the strike had seriously undercut the influence of a minority "hard core" of "old line" guards responsible for harassment of prisoners and their visitors and prejudice against black and Hispanic inmates.

That hard core, they said, dominated the guard union - an affiliate of the American Federation of State, County and Municipal Employees - and attempted to intimidate nonstriking supervisory personnel and guardsmen. Incidents included rock-throwing, splashing paint on nonstrikers' houses and life-threatening phone calls.

Davis and Anderson said they were contemptuous of guards who would lecture inmates about their deeds against society and then indulge in such illegal conduct themselves. And while guards have a right to strike for increased benefits, they said, those had laid down their weapons and deserted the guard towers should have been fired outright.

But state labor negotiators, in settling the strike for pennies more in pay than the guards had initially been offered, unconscionably agreed to limit disciplinary action to a week's suspension without pay for Waupun guards who deserted their guard towers. The same light slap on the wrist was accorded guards at the Ethan Allen School for Boys who threw their keys on the cottage floors and left, causing a riot in which two supervisors were seriously injured before the National Guard arrived. Wisconsin prison officials, who feel they run one of the most enlightened and progressive prison systems in the country, were infuriated by the limits placed on their right to discipline the offending guards.

Yet on balance, Wisconsin is clearly the winner for its strike experience and the National Guard's intervention. The general public, Acting Gov. Schreiber notes, has little exposure to the prison system: "There had never been a cross-section of our citizenry with first-hand exposure to the inner workings of the correction system - never, that is, until a large number of citizens-turned-guardsmen from all walks of life spent two weeks actually working around the clock in our correctional institutions."