For Robert Wilson, citizen of the U.S., legal inhabitant of New York City, native of Texas, this weekend stands as a rare chance to see how his work goes over in his home country.

It won't be a performance on the scale of "Ka Mountain and Guardenia Terrace," the seven-day, 500-person marathon sponsored by the Iranian government in 1972; or "Einstein on the Beach," the vast audio-visual opera underwritten by the French, shipped across Europe and finally given two sold-out performances at the Metropolitan Opera in 1976; or "Death and Destruction in Detroit," the 5 1/2-hour, $1-million affair underwritten by the West Germans in 1979.

But then, his operatic version of Euripides' "Medea," beginning a series of six "open rehearsels" tonight at the Kennedy Center's Musical Theater Lab, is still in the sketch phase, with two-dimensional scenery and taped music. After this weekend, he will set "Medea" aside until the summer of 1982, when he expects to mount the full-scale work in Venice and Hamburg.

"There's no one here to produce a work like that," he comments over a lamb-chop lunch and a glass of vodka at the Kennedy Center's Roof Terrace Restaurant. At 36 or 39 (depending on your source of reference), Wilson has grown weary of trying to explain his work -- his irritation once drove him to say the word "dinosaur" over and over again for hours at a press conference in Yugoslavia. But he can and does complain passionately about this country's indifference to art that isn't traditional, commercial and "nationalistic" -- a tide that seems only to be gathering more force, as David Stockman & Co. argue that the federal government is actually over-supporting the arts by 100 percent or so.

A co-worker describes the lanky, short-haired Wilson as "fawn-like," although, at 6-4, he stands rather tall for a fawn. Describing his profession is harder. Do you call him a playwright, a director, a visual artist, or a painter-choreographer? Wilson has taken to labeling most of his works "operas," but text is a sometime thing with him, while the physical action, scenery, props and visual effects tell stories of their own.

In an era when many artists claim the honor of being "avant-garde," Robert Wilson is the genuine article. He was writing nonverbal plays in grade school. "Psychological" drama has never held any interest for him. Nor, indeed, has almost anything that has gone by the name theater for the last several hundred years of Western history.

At the University of Texas in the late '50s, he began as a business major but gradually devoted more of his time to painting, dance and working with disabled and brain-damaged children. Later he studied art and architecture at New York's Pratt Institute, while continuing to teach body-movement and body-awareness. One of his students, a deaf young man named Raymond Andrews, became the central figure in Wilson's first major work, "Deafman Glance," performed at the Brooklyn Academy of Music in 1970 and then in Europe.

"Deafman" startled audiences and critics with its evocative images -- among them, a black woman wearing a black Victorian gown and one black glove, seen stabbing her children; a giant frog with a fat man and two red-wigged women; an eight-foot Bugs Bunny; a kick-line of black mammies doing a jig; a woman leading a live goat; a paper-mache ox swallowing the sun; erupting volcanoes; crawling fish; apple-eating apes; and Marie Antoinette and George Washington.

"The whole of existence has been condensed here into four hours which bring us to an apocalyptic end," said playwright Eugene Ionesco after seeing "Deafman" in Yugoslavia.

"In my art, the visual element is not decoration," says Wilson, illustrating his discussion by drawing careful charts of acts, scenes and design concepts in an unlined notebook. "It's not background. It's an integral part of the play. . . In most of my plays it's just as important as the text. It's sort of like you have a hero sandwich and you have all these layers. Every layer is independent."

Actors who have trained and struggled to make the physical and visual aspects of their performances complement the dialogue just learn to keep these elements separate when they work with Wilson -- because that's where he keeps them. "The plays are like sometimes we're in a dining room and we can be talking and we look out the window and see something else," he says.

Actors and audiences need to learn new notions about time too, because one of Wilson's recurring devices -- which helps account for the great length of several of his works -- is to slow time down. That idea came to him originally, he says, when he saw a slow-motion film of a mother picking up her baby. Shown at normal speed, she seemed eager to help the child, but as Wilson examined the film frame-by-frame, something else emerged -- a momentary feeling of disgust.

"The mother says, 'Oh, I love my child,'" says Wilson, "but it's not as simple as you think. The body is moving faster than we think."

In the United States, Wilson recognizes he is a special taste. "The problem," he says, "is that we have basically one kind of theater here in America -- the 'boulevard entertainment,' as they say in France, and it's all based on making money." A production like "Einstein on the Beach," his collaboration with composer Philip Glass and choreographer Andrew de Groat, couldn't possibly make money, says Wilson; with a staff of 90 technicians, "Einstein" merely loses more money the longer it runs.

One potential underwriter -- the shahbanou of Iran -- is no longer in a position to help. She came through in grand style in 1972, however, enabling Wilson to work with 500 Iranians and Americans for three months preparing a work that took a week to perform and involved scaling seven foothills on successive nights. "She was a very brilliant woman," says Wilson of his ex-patroness. He also says he is sympathetic to the Iranian revolution, although there were student protests against his presence there and he doesn't expect to be invited back.

After the "Medea" tryout ends Sunday, Wilson will turn to "Parsifal," "Golden Windows" and his biggest work of all, an epic production inspired by the American Civil War, which should take eight or nine years to reach fruition as he heads off to commitments in Australia, Japan, Germany, Italy and France.He will spend the next nine months, and 10 months of 1982, in Europe. His creative energies are booked virtually nonstop into 1986 -- and almost exclusively abroad.

"Medea" is his first adaptation, and he says all of the original Euripedes will be used -- some of it, however, in ancient Greek, some in modern Greek and some in English. "I have followed the text very closely," he says. The production is also on a relatively modest scale by his standards, running three hours with seven principals and a chorus of 12. For Wilson, the idea is to see a rough version of the work in miniature, and he has invited an assortment of producers and Opera House impresarios to see it too, hoping someone will invite him to perform "Medea" in the United States.

"Because I'm an American," he explains. No offense intended to the rest of the world.