"Not too much rice," warns Jean-Pierre Rampal, whose small weight problem is mitigated by his considerable height.

He pauses for a moment, meditating on raw fish -- a high-protein diet if ever there was one. "You do not feel so guilty when you eat sushi," he says. "When I am in Japan -- then I can diet."

Rampal has acquired his taste for Japanese food because of the Japanese taste for flute music. Japan, he says, is "a country where almost every flute player in the world has been invited." He visits there every two years, staying five or six weeks.

In Washington, where he is halfway through a two-week conducting engagement with the National Symphony, Rampal has a new venue for his Japanese style of dieting: the Sushi-Ko Restaurant on the part of Wisconsin Avenue that would like to be called (and almost is) Georgetown. He walked in for the first time a few days ago and five minutes later was an instant old friend of proprietor Kojiro Inoue, who is also a friend of Mstislav Rostropovich. Conversation flowed, in Japanese and French, but mostly in English -- which Rampal speaks almost as well as French and somewhat better than Japanese.

"I speak restaurant Japanese," he says. "That's very important." But he also knows enough other Japanese to say "okini," with a very long "o," to a chef behind the sushi counter.

"That means 'thank you' in the Kyoto-Osaka dialect," he explains as he is handed a particularly tempting morsel. "I am from Osaka," grins the chef, touched by the subtle politeness of a down-home "thank you."

A moment later, Rampal is explaining the Japanese symbolism of the sea urchin in the language closest to his heart -- "C'est le symbole de l'aphrodisiaque" -- and then mixing languages in shock and dismay as a raw pigeon egg starts to slip from its bed of salmon eggs, down past the seaweed wrapper on a salmon-egg sushi: "C'est pas possible! . . . Slippery; very difficult to eat." But with a neat flip of the chopsticks, Jean-Pierre Rampal manages.

When he talks about music, he slips easily into English; the Op. 51 quintets of Friedrich Kuhlau, which he is recording with the Juilliard Quartet, are "beautiful music," he says. "It's like Beethoven; you cannot tell the difference. We are finding a lot of good, unfamiliar material from such composers as Czerny and Moscheles. Small masters of the 19th century; they are not so small. How many composers produce every time a masterpiece?"

A musical conversation with Rampal can range over wide territory. He is not only a flutist but also, as he is demonstrating with the NSO, a conductor. "I conduct all the orchestras in America except the Big Five," he says. "I would be scared to conduct the New York Philharmonic," an orchestra with a reputation for giving guest conductors a hard time. "You know, you can be trahi . . . what is the word . . . betrayed."

Rampal has no specialized repertoire as a conductor, he says: "Whatever they want, I do it, but if they asked for Barto'k's 'Concerto for Orchestra' or Stravinsky's 'Rite of Spring,' I would think for a long time."

One musical job Rampal does not do is composing, though -- at the composer's suggestion -- he did transcribe the Khachaturian Violin Concerto for flute. "Composers are always pleased when you play their music," he says. "You can be a tuba player and play a violin concerto and the composer will be pleased." As a performer, however, he has inspired many composers, and he includes new music in his repertoire -- most recently, concertos by David Diamond and Ezra Laderman.

Of all the composers who have not written flute concertos, he says, he most regrets Tchaikovsky's failure to finish one he had actually begun. "There are sketches, letters," he says. "In Moscow, I asked two times to see the sketches, but they said it was impossible. It is a pity; everything he wrote for flutes in the orchestra is very nice."

Thinking back to the early 19th century, from which he has been finding a lot of neglected flute repertoire, Rampal sounds almost regretful that he missed living at that time, when he might have been a composer, too.

"Most of the flutists then were able to write for their instrument," he says. "They were more complete musicians than we are now. But by the beginning of the 20th century, most musicians had to choose to be either a composer or a performer. . . Now, we are concentrated; we have the feeling that you must be a specialist in something. The generalist has disappeared. Now, we have doctors who say, 'I only know about the eyes.' Music is too specialized; life is too specialized . . . "

Rampal's life hardly seems too specialized. Besides all the musical hats he wears, he has written on Japanese cuisine in the foreword to "The Book of Sushi," published by Kodansha International. In a lightly written but informed and informative little essay, he discusses his favorite kinds of sushi (raw fish on a bed of vinegar-flavored rice) which he prefers to sashimi (raw fish all by itself). Mixing his musical and gourmet tastes, he describes sushi as "a ritual symphony of visual and savory textures."

*His expertise in Japanese foods extends to Japanese liquors as well. At the Sushi-Ko, he orders matsu -- not the usual warm sake served in small ceramic cups, but cold sake served in a watertight little box of light wood, about four inches square with a pinch of salt spread along one of the edges.

"You take a little taste of the salt," he instructs, "and you drink, naturally, from the corner. From the side, it is impossible without spilling." He tilts the box gently toward his mouth, purses the lips that have produced some of the most beautiful sounds of his time, and lets the clear liquid slide gently into his throat, careful to avoid losing a single drop.