Rabbi's book is a best-seller; When Bad Things Happen to Good People, by Harold S. Kushner. New York: Schoken Books. 149 pp. $10.95.

What happens when a good man with good intentions writes a sensitive -- but flawed -- book about a very delicate and perplexing subject?

The answer, probably, is that readers should accept the work for its intentions and the good it offers. But they should also challenge and likely reject the rest.

In a book that has reached the best-seller lists, Rabbi Kushner, a man devoted to his religion and obviously to his concept of God, leaves us with this dilemma. He raises the perplexing question that has troubled countless people who encounter crisis or tragedy in their experience: Why has this evil come to me, a good person?

The Boston-area man of the cloth faced a crisis of faith when he lost his young son, Aaron. And in looking for answers, in Job-like fashion, he came to some interesting conclusions. He dismissed the explanations that somehow he was being punished by God for his sins or that God was testing him, and in so doing, making him a better man.

Rabbi Kushner always believed that God is good and under no circumstances would he visit evil on his children. And even under the grief of loss, he refused to give up his confidence in the goodness of God.

Instead, he decided that there are certain things that are beyond the power of Deity - things that just happen as a result of some ''natural law.'' This imperfect, or less-than-omnipotent God cannot prevent sickness or suffering; he can only alleviate it, Kushner concludes. And he counsels us not to ask God to do more than he is able to do.

Obviously, this rationale will leave many with a more troublesome dilemma than the one posed by this book's title. Why should one trust in an ''imperfect'' God? And how does one measure what is in the scope of Deity's capabilities and what is not?

Countless numbers who have experienced healing from sickness and reformation from sin would take issue with Rabbi Kushner. These people have more than ample evidence of not only God's goodness but of His omnipotence.

Beyond this, the author is to be commended for encouraging people to reject the blaming of God for adversity and encouraging them to turn to a ''loving God'' to give them strength to help themselves and others, particularly in times of trouble.