"My background is peculiar," said Isamu Noguchi, a man who belongs nowhere.

Because the sculptors of America regard him as their dean, he was selected as the honorary chairman of the 11th International Sculpture Conference which closes here today.

Noguchi's presence is uncanny. He somehow seems most serious at those moments when he laughs. His dark-flecked eyes are gray or green, depending on the light. As you meet his glance, the hotel room around you seems to fade. His speech is brisk yet stately. In Japan, Noguchi is known to be American; here he is thought Japanese.

Noguchi has created art of river rocks as well as cubes of steel.There is in his newest work something that feels ancient. He has no single style, no one material holds him. He has worked with marble, granite, glass, paper, clay -- even dancers. Apprenticed to Brancusi once, he has also worked with dancer Martha Graham, architect Louis Kahn, Buckminster Fuller and even Gutzon Borglum, the man who carved Mount Rushmore. "I have been forunate enough," he says, "to work with some key people."

There is in his sculpture a kind of silent hum: an energy that, arcing between opposites, appeases contradictions. The man, too, seems to shimmer. The strangest thing about him is that he seems to have no age.

"Let me introduce you," said the master, "to my friend Nizette Brennam." Brennan, a Washington sculptor, a good one, is now 29.Noguchi is 75. Sometimes, as the two friends talked, they seemed the same age.

"This morning," said Noguchi, "we took a walk to the Botanical Gardens to see the cactuses. One of them was as beautiful as any striptease dancer."

"Now what do you mean by that?" asked Brennam.

"Her spikes were, I thought, daring," said Noguchi. "Her headdress was astonishing. Her color was the color of the finest jade. She looked," he paused, "expensive."

Brennan worked some years ago with Isamu Noguchi at his Long Island City studio. "She was not my student, nor was she my apprentice. We two worked together. She was there," again he paused, "as a welcome thief."

"He told me from the start," said Brennan, "that he was not a teacher. But I learned all the same. Isamu had some pieces there of black Italian marble, and I took one away and worked it and then gave it back to him."

"I am the proud posessor now of an early Brennan. What is stolen," said the master, "comes back as a gift."

Noguchi was born in Los Angeles on Nov. 17, 1904. His father was a Japanese poet, art historian, and professor of English, his mother an American writer. He was raised by his mother in Japan, and returned to this country in 1918 to go to school in Rolling Prairie, Ind. The young sculptor's first statues were sufficiently traditional to satisfy the arch-conservatives of the National Sculpture Society, who elected him a member in 1923.

"My escape from traditional academic sculpture occurred when I was 22, when I went to Paris to work in Brancusi's studio -- where I, too, was a welcome thief. The studio's walls were white. Brancusi's eyes were brilliant. So, too, were Picasso's, but Picasso's were like bullets coming at you while Brancusi's always smiled. He made of me a convert. It was my last conversion.

"Many sculptors seem to undergo regular radical changes. I am not one of them. You must remember that abstractionism in those days seemed a bit too European, somehow un-American. My own solution was not to turn to the American scene -- but to go to the Orient. I spent eight months in China, then returned to Japan.

"While I was in China, I made calligraphic drawings. In Japan I did ceramics. So my discovery of the Orient had to do with their most typical materials -- paper and ink, and clay and the kiln. Working with these things you cannot make mistakes -- or rather, your mistakes become the quality you achieve. It is always the first time. You are always coping with the first mistake. Perhaps all creation is just that -- learning to live with the initial mistake. Think of what God went through when Creation started rolling."

Noguchi's towering reputation is based on many things -- on his carvings with their balanced roughnesses and smothnesses, his sets for Martha Graham, his gardens and his earthworks and his paper lamps.

"I find that young sculptors now, the ones who made the works of art scattered throughout Washington, have, at last, discovered that sculpture is not this, not that, that is may be anything. You see in their work a pointing out of things that have been known for a long while. They seize one small aspect and say, 'Look, what I've found: a whale.' Such things found in innocence, of course, may be enjoyed."

Noguchi's own contribution to the Conference's exhibit -- a column of carved stone -- has been erected on the grounds of the American Institute of Architects at 18th Street and New York Avenue NW. Informed that at least one perhaps prudish viewer thought the work too phallic, Noguchi laughed.

"The Washington Monument out-does her by far. So does any flagpole, so does that lady cactus. The sculpture at the AIA looks feminine to me," he said, "like a violin or a Cycladic carving. See the roundness of her breasts. What difference does it make? After all, the work remains sexually attractive.

"People say my work has that power. Perhaps they smell it, perhaps I have latched on to something beyond form. You must always be alert to nature's organic friction." Again, Noguchi laughed.