Eight American writers and musicians gathered at the Duke Ellington School of the Arts Monday night in a show of support for the outlawed dissident group, the Jazz Section of the Czech Musicians Union.

Keynote speaker Kurt Vonnegut pointed out that plans for the evening had been made long before the announcement of the current summit and that the planners supported the concepts of dialogue and glasnost, which were so clearly violated by last year's jailing of two Prague artists.

Vonnegut objected to attempts to politicize the evening as part of the East-West conflict. The real conflict, he maintained, was a worldwide one between puritans and nonpuritans.

He explained he was using H.L. Mencken's definition of a puritan as "someone who has the suspicion that someone somewhere is having fun."

And there was no better example of pure, unadulterated fun than the set the Mitchell-Ruff Duo played after Vonnegut's speech.

These two jazz musicians have been playing together for 32 years now, and every hour of that partnership paid off Monday night. The sound of Willie Ruff's acoustic bass was made visible on his vigorously bobbing, radiantly smiling face. Dwike Mitchell closed his eyes and rolled his head as if in a half-trance as his strong fingers roamed up and down the keyboard.

Ruff switched to the French horn to play luxurious vocal-like lines against the piano in Mitchell's arrangement of "Lush Life."

Mitchell unveiled a blues he had written especially for the evening, "Jazz Section Stop"; it embodied the irreverent freedom that threatens puritan authorities everywhere.

Sonny Rollins showed up to talk about his experiences playing in Eastern Europe and to express his regrets that recent dental work prevented him from playing. Josef Skvorecky, the Czech expatriate writer, read a humorously dreamy excerpt from his jazz novella "The Bass Saxophone."

Washington novelist Rod Macleish read a poetic open letter to Czech President Gustav Husak about the true nature of sound and silence. Washington's Billy Taylor Trio concluded the evening with a jazz set that found Taylor's light, fluid touch on the piano counterbalanced by the more emphatic rhythms of drummer Bobby Thomas and bassist Victor Gaskin.