THE STORY of Harry Tucker's ordeal might have taken place on Devil's Island -- but it happened in the United States in 1977. Mr. Tucker was just another inmate in Virginia's prison system until he was denied parole in 1976. He reacted to the denial so emotionally that he was transferred to a mental hospital. There he was given a drug by a doctor who did not know how it might affect him. When he suffered a severe neurological reaction, he was given more of the same drug by unsupervised and untrained inmate helpers. When he became paralyzed, he was sent to another hospital where the doctors failed to diagnose what was wrong with him and prescribed a second drug that produces the same kinds of reaction. After he had been totally disabled, he was left unattended in a third hospital for about six months in filthy, maggot-infested condition. Only then did he receive proper medical treatment. As a result of all this, Mr. Tucker is paralyzed, confined to a wheel chair, and without hip joints.

No one disputes the basic facts of this story. The prison doctors and officials all say it was someone else's fault. But the companies that insure them against malpractice have settled Mr. Tucker's suit for $518,000, apparently fearing that a jury might award him even more.

Whose fault was it? The doctors and prison officials must bear the direct blame for treating a human being so callously. But while there can be no excuse for their conduct, there is also some truth in the claim that they are overworked and their facilities understaffed. So the State of Virginia bears blame, too, for tolerating a prison system in which such a thing could happen.

Virginia, unfortunately, is not alone. Its prison system is not among the nation's worst, and there have been efforts in recent years to improve it. But Harry Tucker's ordeal reveals how far there is to go. His story is unique -- in Virginia and elsewhere -- only because of the extent of the damage done to him and because he was lucky enough to have good legal representation.

The size of the settlement in this case should be a warning to all those states that are reluctant to spend the money required to bring their treatment of inmates up to a decent standard. While the insurance companies are paying the bill right now, Virginia will pay it in the long run through the higher premiums its prison doctors and administrators will be charged. It shouldn't take long for the lesson to sink in: It will be cheaper to spend the money to improve the prisons than to spend it to pay the claims of horribly mistreated prisoners.