COULD ANYONE maintain that there has not been a falling off in fiction during the second half of this century? Probably not. The question is why. The answer is complicated. It features two world wars, a cast of thousands (millions!), and two of modern literature's favorite leading men -- Joseph Conrad, the Polish exile, and Henry James, the American expatriate. The two were neighbors in Romney Marsh for several years. Each had declared his respect for the other's work. Nevertheless, they were ultimately at odds on the questions most important to them -- those pertaining to the purpose and function of the novel. Conrad's fiction was peculiarly masculine -- not just in its milieu, but in its purpose and philosophy. And, simply put, James's wasn't. They represent fundamentally different, in some ways opposed, approaches to fiction. As a sailor, a ship's officer, Joseph Conrad knew not just the sea, but also the islands, the ports, the far outposts of civilization and a bit of the dark territory beyond. From what he had seen and experienced, he drew conclusions. From the time Conrad published his first novel, Almayer's Folly, in 1895, he established a basic pattern that he afterward carried through book after book, story after story. It should be clear from such novels as Lord Jim, Nostromo and Victory that he saw life as a test. Or rather, he perceived everything in life as prelude, so much scene-setting and shifting of events so that the great test might take place. You see it plainest, perhaps, in Lord Jim, in which early on a loss of nerve costs a young ship's officer his mate's certificate. Having failed one of life's tests, Jim hopes for another opportunity to prove himself. He finds the chance to vindicate himself on the Malay coast, in a place called Patusan. There Jim wins the respect of the local ruler and his subjects with honest dealing and brave actions, even earns the title, "Tuan," or Lord. But having redeemed himself, he is tested again when a gang of cutthroats comes to plunder the small kingdom. Once again Jim fails the test -- though this time not through failure of courage but rather through bad judgment. There is more than a suggestion of tragedy in all this. For Conrad, through his narrator Marlow, continually emphasizes Jim's high moral character, his strength and his grand potential. Lord Jim is presented to us as a hero. In this he shares much with the heroes of legend -- Arthur, Beowulf, Hercules -- and Jim's story becomes a modern, more realistic version of a form that goes all the way back to The Epic of Gilgamesh, which is to say to the beginning. Obviously Conrad did not invent the form. But if he did not it was certainly propagated through his adherents, disciples and imitators. Following Conrad's death in 1924, a memorial issue of Ford Madox Ford's magazine, transatlantic review, carried a tribute from Ernest Hemingway, in which he declared that if he knew that "by grinding Mr. {T.S.} Eliot into a fine dry powder and sprinkling that powder over Mr. Conrad's grave in Canterbury Mr. Conrad would shortly appear," then, Hemingway said, he would "leave for London early tomorrow with a sausage grinder." Such devotion found its way into Hemingway's writing as well -- not least in his frequent use of that familiar form predicated upon the test, the challenge. Hemingway's men were always being challenged or challenging themselves. They did so plainly in A Farewell to Arms, To Have and Have Not, For Whom the Bell Tolls and The Old Man and the Sea. Under Hemingway's influence -- he had enormous literary clout in his lifetime -- and directly from Conrad, a particular kind of novel began to emerge, one that seemed especially suited to its time. There was in it, if not violence, then the threat of violence. And therefore the moral courage required of the protagonist to do what a man must do, nearly always required a fair amount of physical courage, as well. There were bridges to be blown up, political assassinations to be managed, banks to be robbed for the cause. And writers, quite serious writers as otherwise different as Graham Greene, Andre Malraux, Ignazio Silone and Albert Camus, began to help shape this new novel with works of their own that dealt with just such extreme situations. What was it that made such books as they wrote so suitable for their time? Well, just look at what might be called their time -- measure it as the first half of this century. During that period there were two world wars, revolutions and civil wars fueled by mass political movements as ruthlessly destructive as communism and fascism; there were genocides -- more than one -- and the displacement and internment of whole populations. Considered in this light, works such as Malraux's Man's Fate and Boris Pasternak's Doctor Zhivago seem no more than reasonable literary responses to the events they described. Have things changed so much since then? After all, this half of our century could hardly be described as tranquil. We have had wars. There have been famines. We now possess a whole new vocabulary of environmental hazards, potential and actual, that had never troubled us before. Still, all this lacks immediacy. Time and distance act as buffers. We might be warned not to forget that the threat of nuclear annihilation hangs over us all, but a threat is not reality. The Cuban Missile Crisis is not Hiroshima, and in fact, Americans have not thought seriously about the possibility of nuclear attack for at least two decades. What do they think seriously about? About their own lives, about matters that pertain directly to them. In loftier moments, about personal scruples, responsibilities, trust, "relationships," all the higher concerns of the Me Decade (which has now stretched on to two). WE LEFT Henry James in fundamental disagreement with Joseph Conrad, and suggested he was a writer of fiction of a quite different kind. Even Ford Madox Ford, who idolized him, said, "It was possible that James never wanted to live outside tea parties -- but the tea parties he wanted were debating circles of a splendid aloofness, of an immense human sympathy . . ." Never, in English or American literature, had a writer put such a fine point on moral conduct; James's fictional tea debates centered on such matters as scruples, responsibilities, trust and "relationships." You see my point, of course. Only in leisured, comparatively unthreatened sectors of a society like our own could James and his characters have given such attention to personal and social matters of morality. It was this sector of society he knew and this one that he wrote for. No serious English novelist of his day, and certainly no American, was so tightly bound to the class he sought as readers. When James attempted more than treating the immediate moral concerns of this class, and tried to inform them of what was going on in the world outside their tea party, as he did in The Princess Casamassima, the results were fairly disastrous. If the world and work of Henry James were so narrowly circumscribed, how did he manage to survive into the second half of this century? Not in the usual way. The tradition he established through other writers during the first half of the 20th century (Edith Wharton, E.M. Forster, James Gould Cozzens and, just possibly, F. Scott Fitzgerald) was so thin that it can hardly be said to have kept his name, let alone his influence, alive. No, it was his appeal as the self-conscious artist, the technical master of his craft, the James of the prefaces to the New York Edition, who captured and held the one audience that never deserted him. The survival of Henry James was the work of the academic community; he was kept on ice at the universities until such time as he might better be appreciated. Well, that time has come. The better part of a century has elapsed since his death, and it might be said that his influence has never been stronger -- directly through English departments, and indirectly through such writers as Robertson Davies, John Updike, Gail Godwin, Alice Adams, Marilyn French and a host of university teacher-writers. The presence of female novelists on that list suggests another reason for the rise of the Jamesian novel of moral conduct: It is a form open to women and attractive to them, as the masculine test novel was not and is not. Women -- to generalize recklessly and dangerously -- are less romantic than men (or they are today, at least). They see life less as the great adventure than as the great journey, the long haul; they see it as a subject for discussion and criticism, rather than a scenario for action; they see it, in short, as Henry James did. WHO WRITES that post-Conrad kind of macho book anymore? Not many. Until recently you could point to Robert Stone and Jim Harrison. But both writers' latest novels -- Stone's Children of Light and Harrison's Dalva -- deviated considerably from their earlier work; it is almost as though they had decided to come to terms with the world around them rather than look back nostalgically at Hemingway and his era. They have apparently left the field open to John le Carre, perhaps the last of Joseph Conrad's true inheritors, whose novels provide a mortal test to beleaguered protagonists. To some, le Carre is a mere thriller-writer and does not belong in such company at all. Well, the same might also be said of Georges Simenon, who said his practice in writing was to take an ordinary man and push him to his limit to see what would happen. That same Conrad formula has been tacitly accepted by nearly all writers of popular fiction in the thriller genre -- Elmore Leonard, Charles McCarry, Dick Francis, Gerald Seymour, Thomas Harris and the rest. Thus it may still be acceptable as an aid to manufacturing popular entertainment but is no longer, we are cautioned, to be countenanced as an element of serious literature. If that is the case, then we will have lost something -- and it is that missing component that is responsible for the falling-off in serious fiction during this half of the century. We will have lost the element of heroism and with it the possibility of tragedy. And without the heroic and the tragic, literature could become no more than an advanced form of applied psychology, a kind of therapy-in-print. Something of the sort may already be happening. But very likely it is out of our hands, anyway. When, in The Third Man, Harry Lime contrasts the rich creativity of Florence under the bloody, chaotic rule of the Borgias, with the many centuries of peace in Switzerland ("And what did the Swiss produce? the cuckoo clock!"), he was putting forward a discomforting truth. Perhaps, for us to have the sort of writing we feel we deserve, we must also have another period like the first five decades of this century. God forbid. Bruce Cook is the author of "Brecht in Hollywood," "The Beat Generation" and other books.