"When my first diary was published," said Ned Rorem, "people praised me for my courage and I was surprised. I'm certainly not courageous -- I am a coward. I always say what I mean, but then I run away."

America's most successful amphibious artist -- known both for his prose and for his music -- visited Washington lastnight for the world premiere of his "Nantucket Songs" at the Library of Congress and paused for a quick, subdued conversation between rehearsals and performance. The subdued tone was partly caused by illness ("I have the flu, and today I have no personality at all"), but also by what he calls his "shyness."

"I'm really not outrageous or flamboyant at all," he said almost apologetically -- a man haunted, perhaps, by the shadow his diaries cast. "No matter how I seem on paper, in person I am very shy and withdrawn."

In 1966, Rorem's "Paris Diary" shocked the literary and musical worlds with its unblinking portrait of the artist as a young homosexual, and in that and subsequent books he has established a reputation for speaking the outrageous in such remarks as this one about opera stars from "The Final Diary": Sutherland is a dumb singer of dumb music. Sills is a smart singer of dumb music. Curtin is a smart singer of smart music."

Yesterday, subdued by flu and perhaps the weight of his 56 years ("I am too old now to be outrageous"), he was more merciful: "Most singers are not as dumb as people think they are." Then a spark of brash, youthfull malice came into his voice: "Of course, some of them are very dumb."

Rorem's own music is definitely for smart singers -- the poems are chosen with exquisite care, and his instructions include (besides such traditional terms as "allegretto") more demanding requirements like "brittle and nasty."

Brittle, perhaps, but hardly very nasty, Rorem yesterday was preoccupied with mortality. "I don't like to talk about the periods of my work," he said. "That is for someone else to discuss. When people ask me about it, I always wonder whether they think I am now in my final period.'

Rorem spent his earliest period in France. "Sometimes I think I would like to go back to Paris -- but what I really want when I feel that way is to go back to my youth. And it isn't there any more. Paris is dead -- no more good music is being produced there, no more good paintings. About all they do well now is film."

He looks 20 years younger than his age but says, "If I have a Dorian Gray sort of picture hidden somewhere, it will show very clear marks of depression," anxiety about my work and my future, jealousy of other composers."

His career began in childhood, when "my parents noticed that I was playing the piano better than my older sister, and that when I had learned a piece I did not want to play it over and over again but would wander around the keyboard composing something of my own."

They got him a new teacher, who introduced him to the music of Debussy and Ravel ("it bowled me over") before he know any of the older classics. He did not get to Beethoven and Schubert until his later years, after his taste had settled on modern music and jazz, and his view of them is unconventional: "I think Beethoven's Ninth is a big bore, and I'm not even sure it's a work of art. I hear the harmonies of Bach through the harmonies of Billie Holiday. What others hear as a subdominant chord in a Bach prelude, I hear as a blue note."

Rorem has been winning prizes consistently from the $1,000 George Gershwin Memorial Prize in 1948 (when he was still at Juilliard) to the 1976 Pulitzer for his "Air Music." While composing well over 100 published works (he does not use opus numbers and declined to give an exact figure), he also has turned out eight books and is currently at work on commissions for orchestral music: A double concerto for cello and piano has been finished and will have its first performance next May, and he says he is now "supposed to be working on a cello concerto."

"I would like to be writing more songs," he says, a little wistfully, "but nobody is asking for them at the moment."