<i> Innocence by Penelope Fitzgerald (Holt: $16.95; 224 pp.) </i>

The villa of the ancient and decrepit Ridolfi family outside Florence has, as is fairly common, a line of statuary upon its wall. The statues, however, are of midgets.

The reason why they are midgets is the key to Penelope Fitzgerald’s clever and dangerously beguiling social comedy, “Innocence.” It is the key, for that matter, to the title. The particular innocence is the ability to live in the world and invent it at the same time, and to coast blithely, though not necessarily unscathed, over the gaps where the real and the invented fail to coincide.

The Ridolfis, who built the villa in 1568, were midgets. As the author points out, with a cool precision that is the heart of her comic style, this meant that they were shorter than 1.3 meters and perfectly formed.

The Ridolfis’ daughter was also a midget, and to give her the assurance that she was just what people were supposed to be, her parents kept her inside the grounds. A suitable staff--”a tiny governess, a tiny doctor, a tiny notary”--was engaged. A playmate, who also appeared to be a midget, was brought in.

But then the playmate, Gemma, began to grow. The Ridolfis’ daughter was in anguish. “She knew, after all, that if Gemma were ever to have to go back to the outside world, where no one was more than 1.3 meters in height, she would be treated as a monster.” Regretting the pain but knowing it was really kindness, she had her playmate blinded and her legs shortened at the knee.

By the 1950s, when “Innocence” takes place, the Ridolfis had lost their power to take any measures of this kind, and almost all of their money. They had retained the villa, part of a house in town, and the assumption that one does ones’ modest things and society does its. Had Columbus not established roundness well before the family tradition began, one or another of its members, while traveling, might even now have fallen off the world’s flat edge.

The remaining Ridolfis consist of the aging count, an amiable, oblivious man whose only defect in humanity is belonging to a different species; his eccentric sister, Maddalena, and his only daughter, Chiara.

Chiara is one of the book’s main enchantments. She is quiet and apparently unassertive. Only apparently. In fact, it really is an extreme of independence. Her sense of herself does not require asserting it over anyone else. Returning from finishing school in England, she is taken by her aunt to Florence’s most fashionably old-fashioned couturier. It is a failure; she goes to a dressmaker and invents two gowns of her own that strike everyone else as decidedly odd.

Dressed in one of them, and wearing a glaring diamond necklace, she goes to a concert of indifferently played Brahms. A young man looms up and asks her if she likes it. “Of course not,” she answers, and he is smitten. He takes her outside, and they spend the intermission standing in the warm rain.

The young man, Salvatore, is another innocent. He, too, has a lineage, though of an entirely different kind. He comes from a poor family in the South. His father was a leftist, a worshiper and acquaintance of that saintly, anti-Stalinist Communist, Antonio Gramsci. When Gramsci was jailed and dying, the father took his son to see him.

The experience--like everything else in “Innocence”--was a rebound at an unforeseen angle. It left Salvatore determined never to suffer, go to jail, or risk his health for an ideal. He becomes a neurologist, as if to say: “Feelings, you are only a bunch of little white, perfectly identifiable nerve-strings.” He embraces practicality like a religion.

Salvatore’s irascible common sense is as extreme and unworldly as the eccentricities of the Ridolfis. His stormy courtship of Chiara--she does most of the pursuing--is a wonderful exercise in wrong turnings. Chiara’s statuesque and clumsy English schoolmate, Barney, when she comes over for several visits, manages to elevate misunderstanding from a social disorder to a state of guerrilla warfare.

Fitzgerald is not particularly good at plots or, to put it differently, at destinations. What she possesses is a set of inimitable gaits along the way. You don’t much care where she goes, you simply want to see her move.

She is in the English literary tradition that manages to invent characters in a different culture with perfect naturalness, like E. M. Forster or Paul Scott on India.

The characters in “Innocence” are vivid, precisely because of their ineffectiveness. Nothing they say or do seems to change very much.

People are blurred and shifted by the things they do change--the stonemason’s person is obscured by the white dust he raises; the politician’s, by the expectations he arouses. So, to act or speak without affecting anything is to preserve an original clarity of line. Nobody seems quite to listen to anyone else in “Innocence,” despite the remarkable things that Fitzgerald has them say.

Passionately in love with the initially illusive Salvatore, Chiara telephones Barney and begs her to come to Italy. Barney refuses; she has a love of her own to investigate. Chiara begs her to reconsider. Barney says that she has been reconsidering at the same time she was refusing. It is an economy she practices to keep down long-distance charges.

Dialogue consists of simultaneous monologues. Every voice has to make itself heard against enormous competition: the weather, the state of the crops and whatever else is going on in the other person’s mind.

Fitzgerald, who is highly regarded in England, where she won the Booker Prize, is not well known in the United States, but “Innocence” ought to change that. Her unsettling wit has led English critics to compare her to Evelyn Waugh and Barbara Pym, but that’s not quite it. Her breeze comes from a very particular point in that general quarter, and it carries a weather we have never quite experienced before.