INNOCENCE By Penelope Fitzgerald Henry Holt. 224 pp. $16.95

HAPPINESS destroys the aesthetic sense," remarks the narrator of Innocence, apropos of love. Equally, the happiness of intellectual delight, which is what one is accorded in this novel, may temporarily destroy the critical sense; Innocence is as civilized and intoxicating as a shot of aged brandy, leaving the reader with the same unanalyzable sensation of having briefly tasted perfection.

Penelope Fitzgerald is an English novelist who is relatively unknown in this country but widely admired in her own. Innocence is the first of her novels to be published in the United States; Offshore, for which she was awarded the Booker Prize in 1979, is to be published here in the fall. A satirist of morals and maners, Fitzgerald has frequently been compared with Waugh, Pym, Spark or Powell in the effort to define her particular blend of detachment, sympathy and amusement in the face of absurd or pitiable human behavior. Like them, she is at her driest on the intemperate activity of love, the old conflict between sense and sensibility, impulses and appearances, though her recognition of the disabling pain of wanting "what . . . you can't have" is perhaps more generous.

In fact, the spirit of Innocence, which is set in Florence and takes both Italy and Italians as satirical subjects, might be more accurately described as Giuseppe di Lampedusa a` la Dame Rose Macaulay. A Macaulay-like moral intelligence and compassion is brought to bear on a Florentine scene as plangently sensuous and nonsensical as anything in Lampedusa's Sicily, all moldering villas, eccentric families and fruitless politics. Devotees of either should find the combination irresistible.

Innocence is the contemporary story of the Ridolfis of Florence, a family of antique lineage and reduced circumstances, headed by the old Count, Giancarlo, and his sister Maddalena, both as decrepit as their villa, the half-abandoned Ricordanza. But the Count's daughter, Chiara, a beautiful, guileless child of 18, possesses life abounding. She falls violently in love wth poor, brilliant, thirtyish Dr. Salvatore Rossi, a neurologist from the South, who is seeking to avoid both the machinations of women and the imperatives of his past, particularly of his father's devotion to Antonio Gramsci. (His mother "had baptized him Salvatore in honour of the Saviour, whereas his father would have preferred not to have had a christening at all, and wanted, quite ineffectually, to name him Nino, after Antonino Gramsci, or perhaps Liberazione or Umanita`, or even 1926, since that was the year of his birth and also that of Gramsci's last imprisonment." Such is the unselfconsciousness of this novel that it is not at all surprising to find Gramsci himself appearing briefly, live, among the fictional characters.

The bare story-line concerns Chiara's and Salvatore's mutual and inevitable pursuit and seduction, their wedding and their tempestuous early married life. But the novel is so much richer than its plot, fleshed out with utterly memorable characters. Besides their importunate families, the lovers each have a confidant or mentor, who moderates their salient qualities: hot-headed Salvatore is advised by his practical colleague, Dr. Gentilini; artless Chiara calls upon her equally practical, plainspeaking English friend, Barney, for assistance. Barney herself, a figure of pure, hilarious energy, causes quite a flutter in the Ridolfi hen-house, appalling Salvatore, disconcerting the old Count and inspiring a speechless admiration in Cesare, Chiara's farmer-cousin, who is and remains reticent to the point of catalepsy. A series of opposites is subtly established, in which the creatures of impulse and abandon, like Salvatore and Chiara, are ranged against the disciples of reason and stability, like Cesare and Gentilini and Salvatore's father's old friend, Sannazzaro, who keeps the complex memory of Gramsci alive to the end of the novel.

What all this adds up to -- though not nearly as schematically as I have suggested -- is a moral fable, for Penelope Fitzgerald is at bottom interested in nothing less than the origins of suffering and the possibility of human happiness. She knows, like Salvatore, that the mental pain of unfulfilled desire, in the broadest sense, "is as genuine as pain with a recognisable physical origin." But she also knows, like the legendary midget Ridolfi,"that {pain} was worth suffering to a certain extent if it led to something more appropriate or more beautiful." Images of amputation, of flood-prevention, of plant cultivation, of the philosophy of Rousseau reconsidered, are scattered all through the novel, reinforcing the central debate about human behavior: how may nature be contained, and to what moral end? When all is done, something approximating a final word is permitted to, of all people, Cesare, "trained to . . . tedium" and half-dead with self-denial. Restless Salvatore is distraught again over some misunderstanding with his bride and threatens to shoot himself. He throws up his hands."'What's to become of us? We can't go on like this.' 'Yes, we can go on like this,' said Cesare. 'We can go on exactly like this for the rest of our lives.' "

Yet, for all its moral authority, Innocence is not cerebral. Penelope Fitzerald's wit is exhilarating; her gift for advancing her plot by means of anecdotal digressions guarantees entertainment as well as depth; and she has a true sensualist's feeling for the textures and colors and smells of Italy. In the end, it is these images which linger in the mind after the book is closed: the unpruned roses of Ricordanza, the bitter fragrance of lemon trees and spring fires, of "dry lavender and olive roots," and the way "the river {Arno}, beginning to sink low in spite of the earlier rains, reflected the yellowish light in its yellowish water and threw over the nearby buildings a curious transparency, like a painting on glass."

Elizabeth Ward is the author of "David Jones: Mythmaker."