"I want to have many more years before me -- to write more," French composer Henri Dutilleux says softly, looking out a window of the Watergate lobby into a sunset over the Potomac.

Dutilleux, whose 70th birthday the National Symphony Orchestra will celebrate (a bit late) tonight and Saturday, has enough work lined up to keep him busy for many years, particularly since he works slowly and carefully, refining his music to a high polish before he makes it public. He spent most of the 1960s working on the cello concerto "Tout un monde lointain," which was commissioned by Mstislav Rostropovich and will be performed by him tonight with Hugh Wolff conducting.

"I was working on other things at the same time," he explains if you ask him how a cello concerto he began to think about in 1961 or '62 was not handed in until 1969. And much of the time, perhaps, he was doing his daily work as a composer, waiting for the magic to happen. "Baudelaire speaks of 'work that bears interest, like capital,' " Dutilleux says. "All artists are aware of that; then there is a moment when excitement, enthusiasm takes over your sensibilities. Perhaps inspiration is a thing that exists, but it is very rare, and it comes only after enormous effort."

During that incubation time he was also, without deliberately tailoring the music to a particular performer, getting to know the cellist who would give the first performance in 1970.

"One doesn't really write for a particular soloist," he says, "but one is fascinated by the soloist's qualities. With Rostropovich, it was the unique sound he produces -- the finesse of sonorities in the extreme registers," and his hand, gesturing, goes up to eye level, then higher and higher, like the top notes of a cello soaring to the instrument's upper limits.

"The high notes," he says. "Rostropovich said he gets dizzy up there, and for a while I was using 'dizziness' as a working title; not physical dizziness but dizziness of the heart."

In the great French tradition, Dutilleux still writes music about love, but the music has no words, and he usually doesn't tell people about it. The word he used was not "dizziness" but "vertige"; he is more comfortable being interviewed in French, though his English is workable. "I discovered that 'vertige' is the name of a perfume, and I did not want to use the name of a perfume for my music," he says.

Dutilleux's actual birthday, Jan. 22, was celebrated in Paris with a concert given by Rostropovich and a group of French musicians. At this age (perhaps because his works are few in number), he has still not achieved the level of name recognition enjoyed by two of the colleagues he most respects: Pierre Boulez and Olivier Messiaen. But his music's quality is highly prized by connoisseurs, and he has received commissions from some of the world's most respected performers: the Berlin Philharmonic; the Juilliard Quartet; George Szell and the Cleveland Orchestra, for whom he wrote "Me'taboles" -- also on this week's NSO program, with Rostropovich conducting. He even has a commission (still to be fulfilled) from a fellow composer: a chamber piece for the Ensemble Intercontemporain, which is directed by Boulez.

Dutilleux's latest work, a violin concerto composed for Isaac Stern, has been receiving its first American performances recently in Boston and New York, with Charles Dutoit conducting the Montreal Symphony on tour.

"I follow the orchestra from city to city by plane," Dutilleux says. But now he has settled in Washington for a while, for the belated birthday celebration and some intensive tourist activity -- visiting monuments, enjoying the cherry blossoms, going to the National Gallery "to look at some great French paintings that you never get to see." He is an ardent museum visitor, full of stories about paintings he has loved.

His great-grandfather was "a painter, a great friend of Delacroix and Corot," Dutilleux says. "He once owned the magnificent portrait of Chopin that now hangs in the Louvre; I found this out only after my father's death. I can remember that I went with him to the Louvre and we looked at this painting together and talked about it for a long time, and my father never knew that this painting had once belonged to our family. No wonder I feel a special tenderness for Chopin."

One painting for which he has a story is "The Starry Night," perhaps the most famous Van Gogh other than his self-portraits. "Van Gogh's 'Starry Night'!" he says. "That painting was my inspiration for 'Timbre, Espace, Mouvement,' which I composed for the National Symphony. But then I knew this canvas only through reproductions. I didn't see the original until I visited the United States after writing the music."

Dutilleux did not use the title of Van Gogh's painting as the title for his music because he wants to avoid "the danger of making a musical illustration." He likes to give poetic names to his works, he says, to "give a little hint [une petite indication] to the public . . . but not too much; you must not close down other possibilities. If the title says too much, the listener is given a particular orientation." One title that is precise, though only to people with rather large vocabularies, is "Me'taboles," a technical term, he notes -- applied to "beings that are undergoing a transformation or metamorphosis, like an insect advancing from one stage of its life cycle to another." It is a splendidly apt title for the orchestral variations the NSO will be playing tonight.

Like his "Me'taboles," Dutilleux may still be growing, transforming himself. He feels he has come into one of the most productive phases of his life. "I have not written much," he says. "I have a very small catalogue. The works that count the most for me are those I wrote at the age of 40 to 45 and those dating from the present. Now, I can make the music I want to make.