SUMMIT By D.M. Thomas Viking. 160 pp. $15.95

D.M. THOMAS writes that a coda ought to be farcical or satiric, which is why he offers Summit as coda to his trio of "improvisational" novels on Russian themes, Ararat, Swallow and Sphinx. Thomas' target in this slapstick send-up of a Geneva meeting between President O'Reilly, sclerotic ex-actor with the charm of the devil and the luck of the Irish, and General Secretary Grobichov, dynamic young head of the U.S.S.R., is the silliness of summitry, indeed of the idea of summit meetings, as though these two men, or any two, have the right to weigh in balance the future of the world. Thomas pinpoints the circus quality of such meetings, the crush of press, the media breathlessly relaying as important the least lifted eyebrow or muttered aside -- Thomas' newspapers even hire lip-readers with binoculars. There is good fun, too, with the one-upsmanship of summitry -- whose wife is better dressed, whose smile is more crinkly.

Silliest of all, of course, is that at the center of this maelstrom of attention are simply two men -- O'Reilly, slipping into senility, pursued by the ghosts of an active sexual past, afflicted with a disease of Thomas' invention that causes him to answer a question only after another question has been asked; and Grobichov, calculating, hungry, and clever, not revealing that he has learned English, nor that he travels with a wife whom he passes off as his mother-in-law, and a beautiful daughter, who not only serves as spouse in word and deed, but whom Grobichov dresses as a porn queen, in the hopes of seducing the President. The two men, at O'Reilly's folksy insistence, withdraw to a private cabin to negotiate; here Thomas shows how O'Reilly's stupid bonhomie and Grobichov's rapacity lead to a number of negotiating breakthroughs, not least of which is that O'Reilly cedes California back to the Russians, in exchange for their promise to buy millions of IUDs.

Unfortunately, farce, and satire even more so, only work when they take the wholly unimaginable and persuade us that indeed, perhaps, these men, these leaders are capable of such grotesqueries. When Philip Roth sends Richard Nixon to hell in Our Gang, there is delight in recognizing that if there is a hell, Nixon will probably act there just as Roth describes him. Unfortunately, Summit has no such prescience, as the joke about the IUDs will show; O'Reilly's aides, anxious for a bargaining chip, overhear the President's description of a video game which they take as real, then name the Independent Unilateral Device. O'Reilly in turn, understanding this as the contraceptive, forces purchase on the Russians, which Grobichov accepts because it seems a small enough price for California, and might in any event help stem the increase of Central Asians.

THOMAS, however, ought not to spread one joke out the full length of even so slim a book as Summit, particularly since this joke seems beside the point. The real joke of summits is not that bargaining positions are absurd, but that grown, educated people arrive at them after long deliberation and careful preparation, not through half-heard conversations and weak puns. Thomas, an artist, seems organically incapable of imagining the world of the politico-technocrat well enough even to ridicule it. Not only are his Grobichov and O'Reilly not close enough to their originals to be good caricatures, but Thomas' imaginative skill is such that his two world leaders, rather than being shocking, are almost charming in their human frailty, and so rather than warning us against the presumptions of summitry, make us almost wish that the originals were more like them.

As a Russophile and as a writer, Thomas cannot help but be appalled by the sort of creatures who control the U.S.S.R. and the U.S., yet Summit does not settle any scores. Oddly for Thomas, the rage here seems inarticulate and strangled, the indictments arch and unfounded, and the world he would chastise emerges unscathed and brutish as ever. This coda, though, does nothing to tarnish the three novels which preceded it, and we may safely take Summit for what Thomas tells us it is, the dream of a woman about to die in an air crash. Thomas' Russian quartet also slams into the ground with this final volume, but that only enhances Thomas' point in the whole quartet, that life's beauty lies in the dreaming, as his art so well conveys.

Anthony Olcott is at work on "Red Don," the first-ever joint U.S.-Soviet thriller, which he is writing with Julian Semionov.