BARDOT, DENEUVE, FONDA. By Roger Vadim. Translated from the French by Melinda Camber. Porter Simon and Schuster. 328 pp. $17.95.

THIS SEMI-TRASHY MEMOIR is fun to read, provided you are a French cinema buff. (You are one if you use the word "cinema" instead of movies, if you adored Brigitte Bardot more than Marilyn Monroe, and if you say "vague" rather than "cuisine" when someone says "nouvelle.") Roger Vadim was a successful director during the flowering of French cinema in the late '50s and '60s, but he was not a great one. Instead, he is best known as the man who bedded his leading ladies, turned each into a lookalike of the previous one, and showed the world their attractions in living color and cinemascope.

He discovered Bardot, married her and directed And God Created Woman, the film that made her a sex kitten for the ages. He discovered Catherine Deneuve and had a son with her. He married Fonda, had a daughter with her, and turned her into Barbarella. The subtitle on the book jacket reads, "My Life with the Three Most Beautiful Women in the World." Give the guy credit: he has good taste in women.

Unfortunately, the "life" he sketches is barely skin-deep, if you'll pardon the pun.

Roger Vadim Plemiannikov grew up in Paris, witnessed the occupation of France during the Second World War, and then became a journalist and screenwriter. The character he outlines for himself here is that of a by-the-numbers European sophisticate -- charming, talented, cynical, half-Russian with bohemian aspirations . . . friends of everyone from Jean Genet and Edith Piaf to Giscard d'Estaing and Mitterrand . . . a hedonist who didn't mind marriage and kids . . . world-class race car driver and expert skier . . . good in bed (wth one notable exception). Just the sort of suave fellow an All- American girl would want to spend a romantic weekend with in St. Tropez. She, of course, would be played by Jane Fonda.

Vadim met La Bardot when she was 15 and still a brunette. Almost half the book is devoted to her, yet he offers no new insights into this vamp-child of the bourgeoisie who did not know how to grow up, much less grow old. "I did not invent Brigitte Bardot," he acknowledges, "I simply helped her to blossom." She repaid the favor by cuckolding him during the filming of And God Created Woman, running off with her co- star, Jean-Louis Trintignant. Vadim handled this as a sophisticate should -- he remained friends with both. There is a hilarious photo of Bardot and Vadim here; he is sprawled, barechested, on a mussed-up bed, looking at her. She has her back to him and is looking in a hand mirror. Perhaps narcissism is what Bardot was really about, but we don't learn much more than we would in an average People feature.

After an interlude in which Vadim took up with Annette Stroyberg, a Scandinavian beauty who had his first child, he discovered 17-year-old Deneuve, still a brunette and still a schoolgirl. This, however, was no sex kitten; she was more a sex cheetah, "very passionate under her rather cold exterior." Vadim describes being snowed in at a resort with Deneuve while finishing a film with Bardot. Brigitte walked in on the couple while they were playing "strip billiards." Later, BB warned Vadim, "She's stronger than you. Don't come crying on my shoulder when you're unhappy."

The Deneuve we see through Vadim's eyes is most memorable as the Imelda Marcos of French filmdom. Shoes! Closets filled with them! Again, someone else will have to fill us in on the rest of this well-shod star, if there is, in fact, more to her than that face.

HE MAKES his best attempt at character development in discussing La Fonda, but again, we get cinemaic snips of stories more than probing analysis. They met when she was 24, not yet political, a starlet rather than a star. He was impotent the first few times they were together, he tells us. "I think it reassured her. I became vulnerable and undoubtedly more human in her eyes." In the course of her Vadim years, Jane began searching for causes beyond acting. On a trip to Amsterdam, she exhibited stirrings of feminism when she saw the prostitutes who sit in windows waiting for tricks. On a trip to Moscow, she was terrified by the monstrous May Day procession of tanks and missiles through Red Square. Together in Paris in 1968, they watched on television as Tom Hayden, then unknown to Fonda, led the antiwar demonstrations at the Democratic Convention in Chicago.

The best parts of this book are Vadim's all-too-casual references to the wonderfully fertile French films and actors of his era. This is the man who directed Jeanne Moreau and G,erard Philipe in Les Liaisons Dangereuses, probably his best work, but he tells almost nothing about the picture except its censorship troubles. He and his women were connected in various ways with the likes of Truffaut, Godard, Fellini, Bunuel. Yet he tantalizes us with their names, while dwelling on his own amours. A "Bardot, Deneuve, Fonda" film festival would have been an ideal tribute, rather than this kiss-and-tell bit of fluff.