In ''The Art of the Novel'' (1986), there is a lexicon in which, under the heading of ''Lightness,'' Milan Kundera notes that he has discovered three repetitions in his work of a character's sense of lightness as an oppression or burden. ''Then I consoled myself,'' he writes; ''perhaps all novelists ever do is write a kind of theme (the first novel) and variations.'' It is useful to keep this in mind in reading ''Ignorance,'' a short fable of a novel, for Kundera is working familiar themes once again. Repeating himself is part of his game with the reader, which puts us off guard. Haven't we been here before? To the Czech émigré's return to the rocky landscape of betrayal and lost love, to the playoff between memory and forgetting? The answer Kundera elicits is yes, but each new work should offer more than the slight shock of recognition. ''Ignorance'' presses on beyond stated themes to the rewards of complex and moving variations.  The novel, translated by Linda Asher from the French, opens with a conversation between Irena, a Czech émigré, and her friend Sylvie, who urges her to go back to her country while ''great events are happening.'' After 20 years of exile Irena's life is in Paris but, persuaded by Sylvie's sentimental tears, her thoughts run to literature, to the story of Odysseus, the ''great magic'' of his return. Thus the plot is set in motion. Irena will return with her husband, a Scandinavian businessman setting up an operation in Prague. Her past, with its rejected memories and unrealized desires, will be confronted. But wait. We must often wait in Kundera's novels for his gloss on the story. ''The Greek word for 'return,' '' he tells us, ''is nostos.'' A nice etymological essay leads to the English word ''homesickness'' and to a decidedly antiheroic view of Odysseus' adventures that counters Sylvie's tears and Irena's literary flush. With this entry, erudite and playful, the writer makes his contract with the reader, as he does most effectively in ''The Book of Laughter and Forgetting,'' less successfully in the recent short novels ''Slowness'' and ''Identity,'' where he is overinstructive, at times even pedantic.  Back to Irena, whose mother has visited her in Paris, but with little curiosity about the city or Irena's life. This enclosure in the present of weightless self-absorption is evident again when Irena, attempting to pick up the strains of her past, assembles friends of her youth in Prague only to discover they have no use for her French wines and no interest in her émigré life, much like Odysseus' old crowd upon his return to Ithaca. Kundera is a master of the revealing incident -- that fine wine gulped with tipsy disregard after a good deal of Czech beer. Irena's party is a flop, but even more disheartening is the aspect of her countrymen, who no longer indulge in complaints of personal hardship and political victimization. They have moved on to stories of bourgeois success. Her bleak enlightenment is underscored by the novelist's impassioned account of the émigré as a character on the stage of European history. Building his prismatic novel, Kundera cuts back and forth between the sweep of his contemplations and the particular lives of his characters until idea and story, the public record and the private, are inextricable.  By chance, Irena comes across Josef, who, she imagines, looked on her with favor one night in their student days. ''Ignorance'' tells their parallel stories, for he too has been urged against his wishes to return from exile to Bohemia (Kundera, now identified as ''Franco-Czech,'' does not use the accepted name of his principals' lost country). Kundera claims Josef is ''suffering from nostalgic insufficiency,'' then alters the diagnosis to ''masochistic distortion of memory.'' Indeed, Josef punishes himself, most severely in reading his adolescent diary, which leans heavily on the romantic gibberish of a ''little snot.'' The memory of his home in Denmark runs in his head as a refrain; Irena is endowed with nostalgic dreams. Kundera's fiction is always ingeniously patterned. Here his control is near perfect, granting Irena and Josef the troubling thoughts of their human dimension, juxtaposing the comic and cruel in a music hall moment in which Irena's husband is decked out in a T-shirt with the slogan ''Kafka was born in Prague!''  Both Josef and Irena are assigned a friend, two more counters to play, which may remind us of the writer's admiration for the sense of play in the 18th-century novel. Milada is the only woman who connects to Irena with honest inquiry into her life as an émigré. N., an old Marxist, asks about the 20 years Josef has been gone, but his inquiry is turned away. The tenderness Milada feels for Irena, the political catching-up between N. and Josef, Kundera's continuing entries into his story -- these are strands closely woven, yet the reader knows we are heading for the main event, a sexual encounter between Irena and Josef in which parallels intersect in the novel's trick geometry of coincidence and desire.  Where does ignorance lie? In Irena's nostalgia, her weighty presumption of freedom to reinvent a past that never was, or in Josef's lightness, his emotional distance, the ease with which he dismisses the past? There can be no answer, unless we tag it the tragedy of the human experience, which seems banal, diminishes the story. The story in ''Ignorance'' goes beyond their joyless tryst in a bleak hotel, a disaster readers may anticipate. The erotic note is essential to the impresario, who as always wants to engage us with his arguments. Josef abandons the sleeping Irena with a truly heartless gaze at her naked body. Just as we note this disturbing recurrent theme, the novelist as provocateur cuts us off: ''And to ensure that no one would give her an unpleasant look, he laid a 500-korun note on the counter before the receptionist.''  ''Loneliness'' is one of the unfelt words in Josef's adolescent diary. As the major players exit to their inescapable encounter, it is Milada who personifies loneliness. In this twilight novel, history is denied by Josef's turn from memory and Irena's quest for the future, but Milada, who did not leave Prague, invests ''Ignorance'' with its melancholy, moving conclusion. She remarks that her friend's first marriage, a false move toward freedom, was an ''irreparable mistake committed at the age of ignorance.'' Yes, but that is only half the story. Kundera's characters are not wiser grown old. What does this demanding émigré writer want of us? That we smarten up, observe the art of his balancing act between arguments and story, watch as history with the weight of the past is tripped up by the lightness of the present. ''Ignorance'' is a cautionary tale.
IGNORANCE   By Milan Kundera.   Translated by Linda Asher.   195 pp. New York:   HarperCollins Publishers. $23.95.