"I want not to do costume design -- it takes time away from the paintings."

It was a curious comment from Theodor Pistek, the Czech artist who had just arrived from Los Angeles, where he was awarded an Oscar for his costumes for "Amadeus." In Washington for the opening of an exhibition of his paintings at the Henri Gallery, he agreed, reluctantly, to discuss his costume designs.

But the subject kept returning to Pistek the painter. "A painter is a free man in his creation. He expresses what he wants -- it is his idea and his responsibility. Costume design is a job. In a film, even the greatest personality has to adapt to the theme -- he cannot just do what he wants."

Pistek has nevertheless done it exceedingly well, designing costumes for more than 100 films, the first in 1960, a collaboration with Frantisek Vlacil, a Czech film producer and friend. "Amadeus" was his first American film. For this project it was an advantage being Czech, he said, and not only because the film was shot in Prague. "I live in rococo surroundings with buildings that are rococo. An American could study that and create that feeling, but for me it was a bit easier."

Because Pistek's English is a bit halting, he asked art patron Meda Mladek, with whom he was staying in Georgetown, to act as translator. "If you like me . . . ," he said, charming her in English. She couldn't resist.

His work on "Amadeus" began with a year of study in Vienna and Salzburg. "You must start with the information -- the rest of the job is one's own imagination." About 100 of the costumes were created from scratch, and more than 600 others borrowed from costume houses in Europe, the sizes and styles adjusted under his supervision.

Headpieces became an important element of the "Amadeus" costumes, as they are in all of the films Pistek works on. "They are the crown, the summit, the most important thing," he explained. "Besides, in film you often see figures just from the waist up. The headpiece completes the character."

Director Milos Forman was disturbed by the way the huge rococo wig worn by Constanze Mozart wobbled, affecting her walk. But when Pistek argued that it was the characteristic way one walked when wearing such overscale hair in that period, Forman understood.

Pistek's input continued far beyond the original designs, into selecting the fabrics in Vienna and Salzburg -- "of course they had the best fabrics; it's where Mozart lived" -- and overseeing production and fittings.

"The costumes needed to be tight and elegant, but the actors playing in them for so many hours needed freedom," he said. F. Murray Abraham, who played Salieri, had an additional challenge. Some of Salieri's own clothes were discovered and used in the film, although they restricted the actor's movements, particularly when he was conducting. "He understood and tried to adapt."

There were changes, too, as the shooting progressed. When the tall, slim actress originally cast to play Mozart's wife broke her leg and left the film, she was replaced by Elizabeth Berridge, a small, buxom woman, and her costumes were remade. It made no difference whether the actual Frau Mozart was as ample as the actress. "Whether it was the style of the time or not, it was her figure," said Pistek, adding with a laugh that it was, in fact, stylish to expose one's bosom at that time.

He collaborated closely with cinematographer Miroslav Ondricek (who also worked with Forman on "Ragtime" and "Hair"), discussing colors and costume. When neither was sure how certain fabrics would photograph, they experimented by photographing the dresses on Ondricek's wife in the photographer's basement, using candlelight as they would have in Mozart's time.

Costume is most successful, said Pistek, when it doesn't look like costume. "It should look like something the actor has lived in his whole life." He believes he succeeded with "Amadeus."

Being an artist helps him design. "I solve problems by working them out through the paintings," he said. He reacquainted himself with painters of Mozart's time, particularly Fragonard and Watteau, artists he had studied in school (every artist in Czechoslovakia must study art history at the academy of fine arts). This renewed study touched his costume designs, as well as his own paintings.

Told that the fabrics, the headpieces and the rococo style of his "Amadeus" designs are now a major influence on Seventh Avenue and even on European designers, Pistek smiled and sheepishly confessed that he might like to try designing a couture collection himself. For women, he said -- men, they have no fantasy.

But he caught himself. "For me it is more important to work on my paintings." When he returns to Prague next week, there are five unfinished paintings to get ready for an exhibition in New York in December.