Nov. 19, 1966 was a day that turned from joy to anguish for Rabbi Harold S. Kushner and his wife, Suzette. They celebrated the birth of their second child, a girl whom they named Ariel. But 12 hours later they listened in bewilderment as a pediatrician told them that their son, Aaron, then just 3 years old, was afflicted with a rare and baffling disease and would not live beyond his teens. "I couldn't make sense of what the doctor was saying," Kushner remembers. "After all, we didn't deserve to be punished."

Aaron suffered from progeria, or "rapid aging." It strikes one child in every seven or eight million, and little is known of its cause. Aaron's hair began thinning at 12 months; he never grew taller than an average 3-year-old. By the time he was 10 he was physiologically in his 60s. Near the end, his bodily systems were so weakened that, simply to breath, he often had to stand leaning against his bed all night. When Aaron died in his mother's arms, two days after his 14th birthday, he weighed 25 pounds.

As counselor to some 550 families at Temple Israel in Natick, Mass., Rabbi Kushner, 46, has comforted many people in their grief. Yet, in his own pain, Kushner admits that his once unshakable faith in an omnipotent God wavered. His four years spent in sorting out his feelings since Aaron's death resulted in a moving and thoughtful book, When Bad Things Happen to Good People (Schocken, $10.95), published this month.

"I wrote it for Aaron as a memorial, for myself because I needed to write it and for countless others who have been confused and hurt and who feel that they should be punished by God and be angry at Him," Kushner says. He rejects the idea that God and nature are one. "Nature is morally blind," he writes, while "God stands for justice, for fairness, for compassion." Kushner notes that the "laws of nature do not make exceptions for nice people. That is why good people get sick and get hurt as much as anyone."

"I don't believe," Kushner argues, "that an earthquake is an 'act of God.' The act of God is the courage of people to rebuild their lives after the earthquake, and the rush of others to help them in whatever way they can." In his son's case, Rabbi Kushner points to the kindness of a family friend who got Aaron a baseball autographed by the Boston Red Sox team, and the children who overlooked his appearance to play with him. "People like that were 'God's language,' His way of telling our family that we were not alone."

Brooklyn born and reared, Rabbi Kushner is a graduate of Columbia University and the Jewish Theological Seminary (from which he later also received a doctor of Hebrew literature degree). He was married in 1960, and served as an Army chaplain and as assistant rabbi in Great Neck, L.I. before moving to Natick in 1966. He is also author of a book, When Children Ask About God, which has had two hardback and three paperback printings. For seven years he has been a panelist on a Boston interfaith radio program called Topic: Religion, which attracts around 100,000 listeners weekly.

On the program Kushner spoke openly of his only son who, despite his cruel affliction, was a bright student doing high school level work at a small private school. "He disliked being stared at," his father recalls, "but there was a part of him that was a ham who took special pleasure in getting bit parts in school plays." When asked what he most wanted to do, Aaron listed visits to the Baseball Hall of Fame at Cooperstown and to an R-rated movie (he got both wishes). Only days before he died, he danced with a girl classmate. "I think," Aaron said afterward, "I handled myself well."

His father, mother and sister are working on Aaron's biography, which will be published next year. "We're trying to remain faithful to his identity without wallowing in grief, without becoming professional bereaved parents," Rabbi Kushner says. "Aaron wanted his story to be told."