THE TIDEWATER TALES By John Barth Putnam. 655 pp. $21.95

A REMARKABLE fact about John Barth is his capacity to change, even reverse his creative direction, and this new novel, The Tidewater Tales, is a brilliant case in point.

Twenty years ago in his now famous essay, "The Literature of Exhaustion," he rather grandly pronounced the realistic novel obsolete, and on a later occasion he expressed his deep distaste not only for realism but for reality in general. "Reality," he said, "may be a nice place to visit but you wouldn't want to live there . . . Reality is a drag."

By 1967, Barth had published several works of fiction that represented his own progressive movement away from the relative realism of his early novels toward a kind of writing concerned less and less with literally reflecting experience and more and more with the difficulty of deciding what, if anything, can be considered valid enough to be reflected and which of the possible validities is really valid.

An acute consciousness of this difficulty initially emerged in Barth's work as a paralyzing affliction of Tod Andrews and Jacob Horner, the protagonists of his first two novels, The Floating Opera and The End of the Road. Both men become obsessed with the idea that there is such an infinite number of versions or interpretations of every truth that it is finally impossible to choose among them. For Andrews this perception results in his failure to solve the mystery of his father's suicide, since all the data he has accumulated concerning his father's life turns out to contain equally plausible clues to his motives for ending it. Jacob Horner suffers even more dramatically from a species of catatonia which renders him incapable of taking any action because he is so aware of the massive plenitude of possibilities for action.

In the two very long and complex novels that follow, The Sotweed Factor and Giles Goat-Boy, what Barth in effect does is transfer his hamstringing idea of versions from the psychological situation of characters like Andrews and Horner to the technical interior of his fiction, where versions become not the self-neutralizing perspectives which the characters bring to experience but rather the conflicting ways in which Barth as novelist does the depicting. But after he has put before the reader a bewildering variety of possible approaches to, and interpretations of, the many events in the two novels and then causes them to undercut and contradict one another, nothing solid is left. All the versions have been rendered suspect.

In the title story of Barth's collection, Lost in the Funhouse, a family spends the Fourth of July at an amusement park, and a 13-year-old boy either does or does not get lost in the funhouse, while Barth interrupts the action regularly to discuss alternative ways of carrying it forward. The protagonist of the story, one realizes, is not the boy but John Barth demonstrating why the boy can never enter the funhouse or find his way out of it, be brought to life as a character or made to enter life as a human being. The funhouse with its infinitely magnifying halls of mirrors seemed at the time the perfect culminating metaphor of Barth's own imaginative deadend, the exhaustion of his sense of creative possibility, his ultimate surrender, after venturing beyond the limits of narrative possibility, to an insistent desire to become silent. In the story called "Anonymiad" he said, "I yearned to be relieved of myself . . . I'd relapse into numbness, as if, having abandoned song for speech, I meant now to give up language altogether and float voiceless in the wash of time like an amphora in the sea, my vision bottled."

BUT THEN in Sabbatical, his most recent novel before the present one, something truly remarkable happened. It seemed that Barth in that book had reversed his former advance into neutralizing relativism, which came to a dead-end in Letters, and returned to a certain Barthian variety of more or less conventional realism. At least he seemed to have decided which, out of all the possible realities, was the one with which he wished to deal. The result was that the action of the novel develops along a clear narrative line and establishes without ambiguity the situation and character of the two narrator-protagonists, a couple named Fenwick and Susan Seckler who are voyaging aboard their sailboat from Chesapeake Bay to the Caribbean and back. Along the way they become involved in certain nefarious CIA machinations and other sinister and wondrous events. While to be sure the story does contain elements indicating that the familiar temporizing mind of John Barth is still hard at work, they are effectively subordinated to the strong realistic thrust of the narrative and so provide the book with an agreeable controlled complexity instead of burying it beneath the old fogbank of endless equivocation.

The Tidewater Tales both does and does not mark Barth's further progress toward the clarity of narrative daylight. In fact, taken in terms of its characters and central situation, it so closely resembles Sabbatical that it can be considered, if not quite a sequel to that novel, at least a companion volume. Once again the story is told by twin narrator-protagonists, this time Peter and Katherine Sagamore, who are very much like the Secklers and who are also sailing, although their radius is limited to the waterways of the Chesapeake Bay. They too are involved in a marginal way in CIA activities, and they even have a friend, one Frank Talbott, who once wrote a novel about his and his wife's sailing experiences in the Caribbean, a novel which is actually Sabbatical with the Talbotts renamed the Secklers. In that novel Mrs. Seckler has an abortion. In The Tidewater Tales Mrs. Talbott has had an abortion but by the end has become happily pregnant, even as Katherine Sagamore, who has had a miscarriage, is also throughout the novel happily pregnant with twins. Her husband, Peter, furthermore, will use the experiences they are having in The Tidewater Tales as the materials of a novel to be called, of course, The Tidewater Tales.

Peter is a writer of minimalist short stories and has adhered so religiously to the principle that less is more that he is on the verge of creative self-strangulation. But by making use of the massively abundant materials provided by the voyage, he will presumably enjoy replenished vitality as well as a new belief in the principle that much more is, after all, much, much better.

IF THE SHEER bulk of this novel is any indication, Barth seems now to share this belief and to have undergone a similar liberation -- in his case, from his former obsession with self-cancelling versions. In his performance here he reminds one of Saul Bellow who, after being strait-jacketed by formal restraints in his first two novels, burst out in The Adventures of Augie March into a loose and baggy picaresque saga, an extravagant sprawl of language, and a huge cast of wildly eccentric characters. Barth seems similarly larky and euphoric, gleefully at play in the fields of his own fiction, sporting outrageously with his medium, clearly loving himself as the creator of all this abundance, and adoring his characters as much as they adore one another.

And in truth, while this is not Barth's most intellectually complex novel, it is without question the richest, most ebullient, and technically daring of any he has hitherto written. It is crowded with grand virtuosic effects that seem to have nothing to do with the action except to interrupt it, yet are offered simply because they are such fun.

There are odd excursions into dreams, some of which are uncannily prophetic of the future action. There are encounters with strange exotic people like the beautiful Greek couple who may very well be contemporary incarnations of Odysseus and Nausicaa or like Captain Donald Quicksoat, a contemporary Don Quixote whose adventures, as imagined by Peter Sagamore, occur in the centuries following the end of Cervantes' novel. Scheherazade comes to life to explain why she told her stories for exactly a thousand and one nights and not 62 or 94. The Sagamores carry on conversations with their as yet unborn twins who, as the novel proceeds, grow into fetal characters known by innumerable cutesy names like Fore and Aft, Spit and Image, Toil and Trouble, Fish and Chips, and Blam and Blooey. It is all a delightful romp through fantasy, myth, fiction, and fact, and it is also a hugely joyous celebration of life.

It would seem on the evidence of this remarkable novel that Barth has finally found his way out of the funhouse and back into the world. Or perhaps he has learned to adjust its mirrors so that they no longer give back endless images or versions of his baffled self but instead reflect the reality he once disdained in all its diversity and richness. :: John W. Aldridge, professor of English at the University of Michigan, has written frequently about modern literature and criticism.