Nov. 19, 1966, was one of the best and worst days of Harold Kushner's life. Twelve hours after his wife Suzette gave birth to their second child -- a daughter they named Ariel -- their pediatrician told them their 3-year-old son Aaron had a rare disease called progeria, or "rapid aging."

"We learned that our happy, outgoing son would look like a little old man while he was still a child," recalls Kushner in the quiet, controlled voice of a man who, although he has told the story countless times, still feels the pain anew.

"We were told that Aaron would have no hair on his head or body; he would never grow beyond three feet in height and he would die in his early teens."

This news would be difficult enough for any parent to handle, but for Kushner -- then a young, inexperienced rabbi who had just left his first congregation in New York to lead a 600-family synagogue in a Boston suburb -- it was particularly devastating.

"What I felt most that day," he says, "was a deep, aching sense of unfairness. I had been a good person and always tried to do what was right. More than that, I was living a more religiously-committed life than most people I knew -- people who had large, healthy families.

"I had assumed my side of the bargain, so how could this be happening to my family? If God existed, if He was minimally fair, let alone loving and forgiving, how could He do this to me?"

Out of those churning emotions -- anger, betrayal, bewilderment -- says Kushner, one major question emerged: "Why do bad things happen to good people?"

"Virtually every meaningful discussion of God and religion," says Kushner, 46, "either starts with or eventually gets around to this question. In all of theology, it is the only question which really matters."

Kushner pondered this dilemma as he watched his son grow to old age. At 10, Aaron was physiologically in his 60s, at 12 he bought his clothes in the toddlers' department, at 13 his bodily systems were so weak that, in order to breathe, he often had to stand leaning against his bed all night. Two days after his 14th birthday Aaron died in his mother's arms. He weighed 25 pounds.

After Aaron's death, Kushner stayed away from his congregation for 30 days to deal with his "grief, frustration and rage." Eighteen months later he sat down to write his answer to the question.

When Bad Things Happen to Good People (Schocken Books, 149 pages, $10.95), is, he notes, "obviously the book of a rabbi. But it is not just for Jews." It is meant, he says, "for all those people who want to go on believing, but whose anger at God makes it hard for them to hold onto their faith."

It is a personal book, "written out of my own need to put into words some of the most important things I had come to believe and know. I knew I would write the book, almost from the beginning . . . to redeem my son's death from meaninglessness."

The most common explanation for why bad things happen to good people is that "we deserve," says Kushner, "what we get." Considering misfortune a punishment for sin stems from "our tremendous need to see the world as making sense," he says. "And most of the time it does. But when it doesn't is when we get into trouble.

"It is tempting at one level to believe that bad things happen to people -- especially other people -- because God is a righteous judge who gives them exactly what they deserve. By believing that, we keep the world orderly and understandable. We give people the best possible reason for being good and avoiding sin . . . and can maintain an image of God as all-loving, all-powerful and totally in control."

But this "neat, attractive solution to the problem of evil," he says, "has serious limitations." Chief among them: "It teaches people to blame themselves. We are so desperate to make sense of what happened that we make the victim a victim twice.

"People stunned by tragedy immediately look back to see where it was they went wrong. They may conclude that 'If only I'd observed this holiday, then my mother wouldn't have gotten sick.' It creates guilt even where there is no basis for guilt. It makes people hate God, even as it makes them hate themselves."

And most disturbing of all, "It does not even fit the facts."

The problem with other common explanations for tragedy -- "It teaches us a lesson," "God has a purpose we can't comprehend," "It makes one a better, more sensitive person" -- is that they "aren't really meant to help the sufferer," he says. but "meant primarily to defend God . . . and transform bad into good and pain into privilege."

As the parent of a handicapped child, says Kushner, "I was offended by the notion that God had singled me out because he recognized some special spiritual strength within me. Does that mean if I'd been a weaker person my son would be alive today?"

Instead, says Kushner, "Consider that maybe the suffering happens for some reason other than the will of God." Such as "bad luck, randomness." Aaron's illness, concludes Kushner, was "the result of a blind genetic accident."

This idea that "some things happen for no reason," he says, terrifies some people. Albert Einstein reportedly was uncomfortable with quantum physics and tried for years to disprove it, "because it's based on the hypothesis of things happening at random. Einstein preferred to believe that 'God does not play dice with the cosmos.' "

To those people Kushner suggests: "Perhaps creation -- the process of replacing chaos with order -- is still going on. Suppose God didn't quite finish by closing time on the afternoon of the sixth day. The world is mostly orderly, but pockets of chaos remain. Or it may be that God finished His work of creating and left the rest to us."

This "residual chaos," he says, "may represent that aspect of reality which stands independent of God's will, and which angers and saddens God even as it angers and saddens us.

"We can't explain it any more than we can explain life itself. All we can do is try to rise beyond the question 'Why did it happen?' and begin to ask the question 'What do I do now that it has happened?' "

People who cannot accept this philosophy, says Kushner, are often those who maintain a belief in "the traditional idea of an omnipotent God."

About 10 percent of the calls and letters he's received since the book's release last fall are from "fundamentalists" trying to convert him, about 20 percent from those with other tragic stories and about two-thirds from people thanking him.

"They say things like 'For the first time in 10 years I can go to church again,' " says Kushner. "It's very sustaining."

Surviving a tragedy, he concedes, requires courage. The most helpful survival tools, he says, are "the ability to forgive" and the "ability to love." Ordinary people can do extraordinary things, he says, if they can "forgive and accept . . . a world which has disappointed them by not being perfect . . . (and can) reach out to the people around them and go on living despite it all."