JANET FLANNER once wrote that she was dubbed Genet -- the name under which she composed her "Letter from Paris" -- because New Yorker editor Harold Ross thought it "seemed like a Frenchification of Janet." With this appealing logic, how appropriate that peeking through her last name is the French word "flaneur ," a term that evokes those poetic, down-at-heel walkers in the city, who, with a detached and urbane eye, observe cafe society.

In her meanderings through Paris -- and, as Janet Flaner's World makes apparent, the rest of Europe -- Flanner embodied this esthetic version of the roving reporter. For 50 years, beginning in 1925, her biweekly accounts of the cultural, social and political doings of France were one of The New Yorker's most popular and revered features. In these 2000 to 3000 word "letters" Flanner helped develop a new form of foreign correspondence, one that "dealt not with political news itself, but with the effect public political news had on private lives." Concentrating on "that mixed artistic, monied, demiaristocratic, semimondain Paris circle called le beau monde " she attended all the events of the social season -- art exhibitions by Picasso and Matisse, the trials of the swindler Stavisky and the traitors Petain and Salan, the funerals of the great, including Paul Valery, Colette and Charles de Gaulle. She described the effect on the tout Paris of Josephine Baker in the '20s and James Bond in the '60s; along the way she also composed full-length verbal portraits of Braque, Matisse, Picasso, Malraux, and pen sketches of "Coco" Chanel, Gide and Cocteau, party giver Elsa Maxwell, dancer Isadora Duncan and assorted duchesses and dressmakers. Until nearly the end of her life, last year at age 86, she was still crafting her sentences and paragraphs into what composer Ned Rorem has called her "nourishing one-page meals."

Janet Flanner's World , despite its uninviting subtitle, serves no leftovers; this is four-star Flanner, drawing from nearly all phrases of her career, though concentrating on World War II and its aftermath. Its piece-de-resistance is, inevitably, her long profile of Adolf Hitler, which first appeared in February 1936. Titled "Fuehrer," the essay is compulsively readable and yet peculiarly dated by later events: describing Hitler in New Yorker profile style comes across a bit like a National Lampoon parody. Still, Flanner uncannily evokes the ambiance of the early years of Nazi Germany, complete with Unity Mitford lunching with the Fuehrer in Munich and rumors that Hitler might be homosexual. It is, however, the depiction not of evil incarnate but of a comic opera fanatic: "Dictator of a nation devoted to splendid sausages, cigars, beer, and babies, Adolf Hitler is a vegetarian, teetotaller, nonsmoker, and celibate."

That sentence, which opens her profile, demonstrates the three chief virtues of Flanner's prose: a forceful clarity, unusual and telling detail, and a witty use of sentence structure. Like her friend Gertrude Stein, who claimed that nothing was more exciting than diagramming sentences, Flanner valued grammar and the effects of rhetoric, often toiling for days over her short pieces. Even in her first book and only novel, The Cubical City (1926), one finds already in heady bloom her characteristic devotion to precise description and illuminating metaphor, although here the analogies are so exhuberant and Jamesian that they tend to choke this story of sex and a very liberated young woman. But once Flanner shifted to non-fiction and learned to prune her metaphorical overgrowth, she achieved a much admired mastery of the plain style. (Her Paris Journal received a National Book Award in 1966.) Style is crucial to Flanner's success as a journalist because she writes without two of the usual techniques for maintaining reader interest: She almost never says "I," and she seldom intersperses conversation. As a result, Flanner's artful sentences alone -- in their details, metaphors and syntax -- must carry the reader along.

Many writers covering, say, a bullfight, might describe the proud, Hispanic figure of the matador or explain his elegant movements in the ring. But Flanner will also discover exactly what it is a matador wears and what it costs, while simultaneously contriving to comment on the whole bullfighting business.

"Till the war in Spain a matador got 25,000 pesetas, or $5000, for killing two bulls, but . . . his clothes and outfit -- three banderilleros , three picadores , a valet, their traveling expenses, plus bribes to journalists, which was a high item -- had him down $2000 before he marched into the ring. A swell fighting suit (traje de luces , "suit of light," so-called from its gold or silver embroidery) costs from $300 to $500. A popular matador , with ladies after him and a big public to please, has at least six suits. The embroidery is done by nuns who otherwise specialize in making priests' copes. A fighter has to be valeted, the clothes being too heavy and tight to get into alone. It takes a full hour to dress him carefully in the following unvarying routine: First, three pairs of stockings -- elastic, thick white cotton, then rose silk ones ( $12 the pair). Then longish drawers with knee tapes to hold the stockings. Then a linen shirt, formerly of embroidery but now pleated plain, and with strings to prevent its riding up (a hanging shirt-tail can catch a bull's horns and bring death). Then the trousers, thick tricot and so tight that the valet hauls up while the matador jounces down. The trousers have further stocking-holding knee bands, also an inner abdominal girdle to hole in the fighter's stomach; his shape is important in the ring. Next the eyeleted pumps . . . Then the false coleta , or pigtail, fastened to the back hair by a chenille-coverned metal button. Then the sequined vest and finally the coat, weighing twenty-five pounds, of three thicknesses of buckram beneath massively embroidered stiff satin. The sleeves are not sewed in, but are left free under the arms for action and sweat, and are attached to the coat's shoulder by cords running through eyelets. The cape for the march into the ring is pale satin, often embroidered with pansies, morning-glories, rosebuds." r

What is so good about this description is that one sees the matador differently, more precisely, after reading it. Faced with a potentially tedious listing, Flanner carefully modulates her tone, ranging from the elegant Spanish "traje de luces " to the almost vulgar "swell" and "jounces." At the same time that her details make the matador mildly ludicrous -- three pairs of stockings, abdominal girdle, pigtail -- she also manages to invest him with the sacerdotal. His satin embroidered clothes resemble nothing less than the vestments of a priest. Yet he is nonetheless a superstar, "with ladies after him." The entire form of description, the careful enumeration of steps, also transforms the action into the ritualistic armoring of a hero for an epic battle, a battle in which death can come from the smallest detail overlooked, even a shirt-tail riding up.

Although the war dominates Janet Flanner's World -- in the portrait of Hitler, the dramatic relation of "The Escape of Mrs. Jeffries" from occupied France, and the account of the Nuremberg trial with its international cast -- the book provides examples of all the forms of journalism at which Flanner excelled: Profiles of artists -- Thomas Mann, Bette Davis; social scandal -- the Ingrid Bergman-Roberto Rossellini love child; concert reviews -- Casals in Prades, music festivals in Salzburg; courtroom drama -- Nuremberg; reports on the avant-garde -- the neo-realist Italian cinema; and memoirs of the '20s -- Sylvia Beach, Colette, Alice B. Toklas.

Anyone who loves France or good writing will want to visit Janet Flanner's world. In it the now legendary are still young and unknown, Waiting for Godot is only "a curious and interesting play," and Genet Flaneur still happily wanders the streets of Paris.