THE CATHOLIC. By David Plante. Atheneum. 151 pp. $11.95.

EVER SINCE he published the first of several novels about the French- Canadian Francoeur family seven years ago, David Plante has walked a thin line between observation and self-absorption. At times his spare, deliberate prose was as lucid as rainwater, fluid in the way it moved from episode to episode to reveal a sense of a large, troubled family and the city they lived in, but when his characters were unwilling to look beyond anyone or anything around them, his fiction became murky, thick with pointless chatter and sentimentality.

In his latest work -- a novella about a young man's tortured sexual passion for another man -- Plante has unfortunately sided with his less generous and interesting instincts. In fact, the degree of self-absorption here in young Daniel Francoeur alante describes him is numbing, at times, I'm afraid, comical.

Daniel is an avid reader of Walt Whitman, quoting him throughout as a spiritual guide. In college Daniel apparently thought it wrong to think about himself and his body so much, but his popular college roommate, Charlie, knew otherwise and introduced him to Leaves of Grass and, only several lines later, to a night of sex. A couple of paragraphs later -- all of this in the first five pages of the book -- Dan experienced one of the quicker, and stranger, conversion experiences known to contemporary literature:

"The image of Charlie's body relieved me from all my past thoughts and feelings. My soul came alive in me, and I honestly imagined I was starting a new life. What was promised was that my new life would be made by going away, which was to go into the world around me, inhabited by people whose relations with one another were free."

Charlie later marries Roberta, and the couple serves as an anchor for Daniel, who continues to struggle fitfully in his personal life while teaching English to foreigners in Boston. At a bar one night, Daniel meets Henry. They spend the night at Henry's place going through a series of endless sexual gyrations. None of it can be quoted here -- be thankful for that at least -- but suffice it to say that nary an act in the homoerotic catalogue is left unexplored.

That night is the emotional center of the novel; it will quickly become an obsessive memory for Daniel, but there is nothing memorable about it. The sex is joyless, clinical and interminable, and, remarkably, the descriptions are as dull as pulp erotica. It is hard to believe that the writer is David Plante, author of the best parts of The Woods and The Country.

There is one burst of wisdom amid all the writhing and groaning: "There was in our love making, somehow, an awareness of the vanity of it, and admitting the vanity was admitting everything. There was nothing beyond the love making, however violent it was." But Plante does nothing with this. Instead his character idealizes Henry, makes him into some misbegotten version of the ideal man. Or of something. It is never quite clear. All that is clear is the vanity: "He was beautiful, and we were, together, beautiful. His having been in bed with me made me as beautiful as he was, because he wouldn't have gone to bed with anyone less beautiful than himself."

At the beach, Daniel gazes over at Henry and thinks "we were blessed as loving comrades by the blessing of our nation's greatest poet."

Daniel, I think, misreads Whitman, and misreads him in a way that may explain why he is such a dull and confused fellow. Whitman may have celebrated all varieties of sexual love, but he did not content himself with narcissism. Whitman saw his own body as both a reflection of the universe and a part of the universe. He was capable of "comradely love," erotic love, self-love. Whitman, as a literary character, was large, containing multitudes. Daniel reads Leaves of Grass for only a fraction of what the poems actually are. They comprise a man in all his completeness, for all his strangeness.

Daniel ends his own book in poorer health, and seems to have learned little from his experience. So deep is his frustration with Henry, who refuses to turn one lyric night into a Whitmanian epic, that Daniel humiliates himself at a party. He has sex with a young man named Tom as the crowd cheers.

It is here that Plante's minimalist prose has the most parodic effect. As Daniel zips up his trousers, the host wanders over "carrying two fizzing high-ball glasses which he gave to us, then, slapping us on our backs, he said, 'You're all right, you're really all right.' I drank, thinking there was nothing else I would do if I got drunker. While I talked to the host, Tom walked away."

End of episode. The final pages are less eventful. And that is a very good thing.

The Catolic is a poor story, badly written and weakly considered; it has precious little to say about love, homosexuality, obsession, the city of Boston, even. That David Plante has gone astray here should be apparent to even his most ardent admirers. Here's hoping that he will find his way back to the voice and intelligence that provided so much pleasure and promise in the earlier Francoeur novels.