The list of books by Will Oursler, son of Fulton Oursler, would not prepare his readers for this latest novel. For his subject- treated with considerable sympathy and understanding -- is that of a man, a professed atheist, whose non-conformity to the norms of a so-called Christian world brings the destruction of all that means anything to him. Even the philosophical argument, which permeates the story, and the somewhat inconclusive finale, would seem antipathetic to a man to whom a profession of faith was basic to survival in our world. And yet Cliff Murchison, sports car salesman, who defies faith in God, is the one wholly credible character in the cast. His one- time friend, Father Bill Austin, is a mass of contradictions -- even his Christianity is of doubtful acceptance; Julius Schrap, free thinker, is a figure of tragedy, his rebellion bringing him only negation; Myra R., a ""tramp, "" proves able to meet need in human terms; Mrs. Willoughby- most difficult of all to credit- uses spells to work her powers; and Diana, who at the end brings about a possible concession that will solve the problem of Cliff, the boy Joey and herself, somehow never quite rings true. In its summation, however, this is a fairly potent debate -- pro and con belief in God -- that may challenge believers and non believers alike.