New Walker Percy novel: comedy shot through with serious concerns; The Second Coming, by Walker Percy. New York: Farrar, Straus & Giroux. $12.95

In Walker Percy's apocalyptic 1971 novel, "Love Among the Ruins" (subtitled "the adventures of a bad Catholic sometime near the end of the world"), grass is growing through the pavement, and the disconcerting cry of wolves can be heard in Suburbia.

His latest novel, "The Second Coming", a comedy shot through with serious observations, also offers evidence that the end of the world isn't far off, but somehow only the hero, Williston Barrett, seems to notice.

Barrett's problem is that, while everyone around him seems totally absorbed in "a busy round of work and play," strange thoughts occur to him, almost as if dictated by some other voice. This sympton is accompanied by an odd infirmity that makes Will black out momentarily, stumble, and then, in a prone position, he reminded, in vivid detail, of a puzzling scene from his past.

The malady is accompanied by another problem. Though a Rotary Club man-of-the-year, a distinguished retired Wall Street lawyer, an heir to his wife's millions, Barrett isn't sure that life is worth living. He has lost the conviction that action has any connection to will or desire.

His malaise inscribes itself upon the world, which seems more and more senseless, and he feels depressed without knowing why. Who or what is to blame?

When at one point Barrett is shot at in his garage, he's disappointed to discover it was a stray shot from a poacher's rifle: "If there's no enemy, then I am either mad or living in a madhouse."

In a fleeting moment while actually contemplating suicide, he muses, "Yes . . ., that is one way to cure the great suck of self, but then I wouldn't find out, would I? Find out what? Find out why things have come to such a pass and a man so sucked down into himself that it takes a gunshot to knock him out of the suck. . . ."

The stranger with whom Barrett tries to sort out the riddle of his ennui isn't so much troubled by recollections as by what escapes her memory. Allison Huger is an escapee from a mental institution, still suffering temporary amnesia said to be produced by electric-shock therapy.She is trying to come to terms with the world and to begin a new life in an abandoned greenhouse on a secluded piece of property near the Barrett estate.

Out of the chance meeting of two such implausible characters, Percy manages to create a superb novel. A clue to its design lies embedded in the novel's opening words, "The first sign . . . ." This idiom reflects the serious philosophical interest that has marked all Percy's work. His first book of essays, "The message in the Bottle," deals with questions about the nature of signs and semiotics. The characters in Percy novels often act out problems defined in his essays.

Hence, in "The Second Coming," as in his other works, a comic tone overlays serious philosophical-theological themes. It's as if Percy, an MD who gave up his practice in 1942, were conducting small-scale psychology experiments, studying the modes of thinking and of perceiving the world through literature.

Barrett's strange thoughts, couched as they are in believable emotions, nonetheless bear a direct, surprising relationship to Percy's intellectual interests. In an essay, "The Loss of the Creature," or example, Percy discusses strategems for getting off the beaten track, for breaking through the system of symbols that keeps man from seeing the world in its raw and primitive beauty. Contending that humanity's view of itself is incoherent, Percy complains that while, on the one hand, man believes himself to be an "organism in an environment, a sociological unit, an enculturated creature . . .," "man is also understood to be somehow endowed with . . . reason freedom and intrinsic dignity." Percy's hero/quester typically looks for ways to get back to a sharp vision of the ordinary world.

Thus Will and Allison's strange afflictions strip away the conventional and allow them to see everything as if for the first time.

But the protagonists' quirks of mind often make the language of "The Second coming" seem stiff. If Will's mode of speech seems slightly out of sync with the world, Allison's seems to have come from another planet. As they swear their love to each other, for instance, Allison uses a kind of asylum code: "Tell me the single truth, not two or more separate truths, unless separate truths are subtruths, unless separate truths are subtruths of the single truth. Is there one truth or several separate truths?"

Later in the novel, Percy's style changes, reflecting Will and Allison's growing ability to communicate with each other. Wild, comic dialogue punctuates the end of the story.

Percy never explains the book's title, though viscerally, by the end of the story, the reader feels that some kind of promise has been fulfilled. A Roman Catholic himself, Percy is carried beyond sectarian theology by his imagination. What both of his characters discover are ways of breaking suffocating habits of thought and conceiving a new life of adventure with each other

This is a strong novel which satirizes both an easy, ill-considered Christianity and various clinical ideologies, defining its adversaries in modern culture clearly and taking them on directly. "The Second Coming" treats two characters who are suffering because of their age's impoverished view of the possibilities of human life, and it sees them through to a full recovery.