Sphinx <i> by D. M. Thomas (Viking: $17.95; 248 pp.) </i>

“Sphinx” is the third set of reflecting mirrors in D. M. Thomas’ four-part fictional construction. Largely set in the Soviet Union, like “Ararat” and “Swallow,” it continues his play of art and reality, of personage and impersonation.

The mirrors--characters who are, by turns, real and fictions devised by other characters--are as numerous as ever. They do not reflect as much light. “Sphinx” has less dramatic presence than “Ararat” and less wit and invention than “Swallow.” It begins strongly, but by the end, Thomas’ devices are flagging considerably.

Nonetheless, the author’s ability to fascinate remains. And with his quartet three-quarters completed, it becomes clear what a remarkable achievement it is.

Thomas’ use of picture-puzzle clues, twists of identity, sudden and unexpected associations, and plots within plots, is certainly not unique in modern fiction, though his style, with its mordant wit and strong poetic grace, is entirely individual.

But these things are at the service of a deeper accomplishment. As few other Western writers even attempt to do, Thomas has found a way to bleed the large and terrible events of contemporary history into the emotions and fantasies of his characters.

The collective unconscious and the individual subconscious are virtually fused. What is in the air is also in the heart, the loins--Thomas is actively sexy--and the nightmares. It is as if starvation in Ethiopia or the breakdown of the Reykjavik arms talks were to infiltrate the emotional and psychological world of a John Updike or Anne Tyler character in Boston or Baltimore--and pop up suddenly to disrupt their destinies, as well.

“Ararat,” and the tetralogy, begins when Rozanov, a successful, liberal, weak-kneed and self-indulgent Soviet poet, has a tryst with an admirer. She turns out to be blind as well as older than he had thought. To pass the time until morning, he improvises a long poem about another improviser, whose own poem is about a third poet, Surkov. The latter’s fame, flamboyance, lechery and opportunism remarkably resemble Rozanov’s.

This initial set of mirrors generates a whole series of characters--many with mirrors of their own--and themes. There are other poets and improvisers, and a good part of the three books consists of their recited improvisations. Rozanov himself, as it will unreliably turn out, is a fictional improvization.

Pushkin appears and reappears; so does the avant-garde theater director, Meyerhold; so do Beria and Stalin; so do Rozanov’s wife, Nina, and his longtime mistress, Sonya; so do the real and invented Surkov’s real and invented wife and mistress; so do a number of other characters. These include literary bureaucrats, a dissident general and visiting foreigners.

Over the febrile maneuvers of these characters--their loves, quarrels, travels and schemes to win favor or stave off ruin in the morass of Soviet life--looms a steady symbol. It is Mount Ararat, between the Soviet and Turkish portions of Armenia. There are continual, seemingly frivolous references to it. Rozanov is partly Armenian, so are some of the Americans; there is talk of holidays in Armenia; Ararat brandy is continually served.

In the Bible, the mountain was where Noah’s ark came to ground and humanity was renewed. Armenia, site of a massacre of Holocaust dimensions, was where humanity was lost. Nothing, however trivial, squalid or absurd in the lives and dreams of Thomas’ characters, is unrelated to humanity’s choice of salvation or destruction.

In the two earlier books, Thomas’ poetic gifts made his demands on this potentially cumbersome symbolism yield magic. In “Sphinx,” it is used in a faintly tired, almost automatic way; symptomatic, perhaps, of a more general dwindling of energy. We become more conscious of the author’s mechanisms; perhaps because they are accomplishing less.

In quick montage, we see Rozanov embroiled in the complications of his love life; the psychiatric hospital that he will later be sent to, more for untidiness than dissidence; and Meyerhold, who was shot by Stalin, directing a play about such an institution. The central image, which Rozanov--as writer, not character--is working up, is a scarf; the one that accidentally strangled the dancer Isadora Duncan in a motoring mishap.

In Rozanov’s version, the scarf went to Isadora’s husband, a Russian Futurist poet who hanged himself with it when Stalin began to crack down. It passed to poet’s second wife, an actress, who later married Meyerhold. When Meyerhold’s theater was shut, she was found stabbed to death, wearing the same scarf. And Meyerhold himself wore it when shot in the back of the neck in prison.

The scarf is a link binding up Soviet history. There will be other such complex links in the second and principal section of the book. This deals with a left-wing Welsh journalist who visits the Soviet Union and becomes tangentially mixed up in the lives of the Rozanov circle.

He falls passionately in love with Nadia, a former actress and, seemingly, a dissident. In fact, she is connected to the KGB, and her ostensible love for the Welshman masks a whole series of other complex purposes. By the end, she will be in Rome, seducing, on instruction, an aged priest who is the Pope’s confidant, and finding herself, in her turn, genuinely in love with him. Back in London, the Welshman, mirroring the fate of the aimless intellectual Rozanov, will be committed to a mental hospital.

There is comic richness and shrewd paradox in the wanderings of the Welshman, a by-no-means-innocent abroad, among Soviet complexities. His love affair with Nadia is astonishing and moving, until it is deflated by her double-agentry.

Themes of manipulation, deceit and self-deceit dominate the latter part of the book. They tie an excessive number of knots in what is already complicated; and the use of verse to set them out creates an artistic and thematic traffic-jam. More seriously, it narrows the emotional focus drastically. The author’s balance of cleverness and imagination turns uncharacteristically arid.

Taken together, though, the three novels emerge, more clearly than ever, as a work of substantial as well as formal artistry.

It is not by chance that Thomas has placed them in Soviet society. The ability to connect the public nightmare of our time with a sophisticated vision of its individual psychic consequences is characteristic of Eastern European fiction. It is almost entirely lacking in the West.

By nature, perhaps, we would prefer to be idiots in the Greek sense of the word. But when the state or some equally dominating social order invades our lives, our imaginations are goaded first, to propitiate it, then to encircle it and, finally, perhaps, to subvert it. Thomas’ improvisers, scalawags and dreamers do all three.