AN OCCASION OF SIN, by Andrew M. Greeley, G.P. Putnam’s Sons, 351 pages, $19.95.

That the Rev. Andrew M. Greeley, a Roman Catholic priest, would write novels “about sex” leaves some people scandalized — but not so scandalized that they don’t buy his books.

In approaching Greeley’s works of fiction, it helps to know something about this Chicago-Irish priest-sociologist-author, whose non-fiction works, by the way, outnumber his novels by at least 3 to 1.

Though an author for many years, Greeley made his name as a “popular” writer with “The Cardinal Sins,” the story of a priest who never seemed to repent his sexual exploits.

It’s true that Greeley has been known to discuss the possibility of optional celibacy, especially in these times of declining numbers in the priesthood. But Greeley has never suggested that he or any other priest should violate their vows of celibacy, nor does he advocate promiscuity among laypeople. His strong belief in marriage is evident in many of his later novels.

Further, his recent “Faithful Attraction,” a sociological study, offers the good news that faithfulness in marriage is a good deal more widespread than the media would have us believe.

But readers still get distracted by racy scenes in some of his novels, despite Greeley’s contention that the books are not “about sex,” per se. He calls them “stories of grace.” And sexual relations, he maintains, are, in a human way, illustrative of the power of God’s passion and love for his people.

To be sure, “The Cardinal Sins” has a scandalous plot. But Greeley has pointed out that the pivotal scene in his first novel has nothing to do with sex, but is, rather, a long overdue confession of one of the women in the story. And it also could be argued that despite the central presence of the errant cardinal in the book, the real hero is the other priest, Kevin, who does manage to keep his vows.

“An Occasion of Sin” is also the story of two priests — a cardinal who dies a martyr in Central America, and the priest assigned to look into the cardinal’s life to see whether there are events which would prevent his being considered for sainthood.

It is not automatic that cardinals receive this consideration, as Greeley would be the first to point out. But the possible canonization of Cardinal John McGlynn does become an issue when an apparent miracle is connected to the prelate.

Of course, there is a woman involved, a friend whose relationship with the cardinal may, or may not, have been platonic. To further complicate matters, the investigation is being conducted by Father Laurence McAuliffe, who never had any use for the cardinal during his earthly existence.

McAuliffe is a welcome presence in the novel, from my point of view, since he was a central character in my all-time favorite Greeley novel, “The Cardinal Virtues.” I do think it’s stretching a point to suggest that a full-time pastor would have so much free time to pursue this investigation, even given the able assistance of his hotshot, obnoxiously bright curate. (The clergy in this paragraph keep their vows, too.) But such is literary license.

Some of Greeley’s earlier works were steamy enough that I found them offensive, but there seems to be less of that in his more recent novels.

Those who would really want to know where Greeley comes from should read his autobiography, “Confessions of a Parish Priest.” That volume contains many insights into the man, as well as commentaries on some of his novels.

One of Greeley’s recent works of fiction, “Love Song,” really fooled me. Involving two lawyers who fall in love, the novel seemed to offer lust and betrayal and not much religion.

Then came the last chapter, with a Good Friday sermon by the venerable Monsignor Blackie Ryan. The difference between Peter and Judas, Father Blackie suggested, was that Peter accepted Jesus’ forgiveness and love, and Judas did not.

Whether it’s appropriate for Andrew Greeley to write as he does about lust and sex, I don’t know. That’s between him and God.

Most of the people who criticize Greeley’s books don’t read them. The same could be said, I suppose, of many people who criticize the Bible.