Fiction from three 'world class' writers; Over-intensity saps Murdoch's complex saga; The Philosopher's Pupil, by Iris Murdoch. New York: The Viking Press. 576 pp. $ 17.95.

If a reader of Iris Murdoch's earlier work were given this novel with the cover torn away so that there was no way of knowing who wrote it, he or she would nevertheless soon guess the author's identity. There is that same unrelenting Gothic intensity in the book's emotional territory that was present in ''The Sea, The Sea'' - the novel that won Iris Murdoch Britai6's prestigious Booker McConnell Prize in 1978.

From Page 1 of ''The Philosopher's Pupil'' onward, we are in Murdochland - called Ennistone, an English spa town where emotions bubble and boil like the Ennistone hot springs, and the danger of drowning, physically or emotionally, is never far away.

Unfortunately, this time it's a bit too much. Miss Murdoch seems to be afraid of boring her readers, and so she exaggerates her characters and develops her plot by jarring leaps. Many readers may find this determined intensity unrealistic and exhausting.

Still, Iris Murdoch must again be credited with tackling serious themes in this, her 21st novel. As usual, her central theme is the search for a definition and realization of love. Miss Murdoch was a lecturer in philosophy at Oxford, and she weaves discussions of philosophy and religion into the novel's narrative with only mildly self-conscious results.

As the title implies, the central relationship in the book is between a distinguished, elderly philosopher, John Robert Rozanov, and a former student, the failed and intermittently violent George McAffrey. But this central relationship is totally one-sided: The pupil longs for the attention and approval that the philosopher is determined to deny.

If the novel had focused more narrowly on this conflict, it would have made a very interesting book. The secondary plot, which concerns Rozanov, his granddaughter Hattie, and George's younger brother Tom, would have provided a sufficient counterpoint.

But Miss Murdoch is fond of complexity, and so she thoroughly populates her town of Ennistone with a succession of unappealing minor characters. She seems determined to explore to no avail all manner of unlikely relationships. It is here that the reader may ask why it is that modern fiction spends its time exploring the perverse, the extreme, and the negative - a good question, which ''The Philosopher's Pupil'' doesn't answer.

But if Iris Murdoch falls short in her characterizations in this novel, she is best in her descriptions of places. From her first mention of Ennistone as ''a rather self-satisfied little place'' through her descriptions of the complex system of springs and baths which comprise the ''Institute'' where fraught Ennistonians hope to soothe themselves, we see the work of the considerable writer Iris Murdoch is supposed to be. And near the end of the book, when Tom McAffrey becomes lost in the inner working of the baths, Miss Murdoch has somehow managed to sum up in one elaborate, Dantesque image the psychological content of the entire novel. An example of what Tom sees when he goes down to find the source of the springs:

''The stairways, of which he could now see more, were made of some kind of light, faintly flexible metal, presumably steel, but some kind of exquisite steel, Tom thought, since they were so elegant and spidery, almost insubstantial , with their narrow treads and eye-defeating lines of thin vertical rails supporting slanting bannisters, more like suspended trapezes than stairs. . . . He had noticed no sidewalls and could see none now as the steam was a little thicker. The whole contraption, with him upon it, seemed to be hanging in space.''

It is touches like these, and the occasional worthwhile human insight, that make one feel ''The Philosopher's Pupil'' could have been an excellent novel. It is puzzling that the author and editor allowed it to overshoot this goal - and fall into the deep end.

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