A brightly hued abstract by the late Morris Louis, the best-known member of the Washington Color School, fetched $385,000 here tonight at an auction of contemporary art. The Christie's sale of 65 lots for $4.24 million set records for Abstract Expressionists Franz Kline and William Baziotes.

"Mu" (titled after the Greek alphabet character), a 102 3/4-by-181-inch acrylic on canvas, fell short of the Louis auction record of $473,000 for "Sigma" (1961) in May 1984. It was consigned by the Irving Formans, Chicago art collectors.

The winning bid appeared to have come from Richard Weisman, a New York collector and banker who advises Andy Warhol Enterprises, but he refused to comment.

"Mu," from the artist's sought-after "unfurled" series, was painted the year before the Baltimore-born Louis died of cancer at 49 in 1962. In the painting, intense rivers of color -- orange, brown, yellow and black -- flow from the edges of a canvas whose center remains blank.

Although grouped with the Washington Color School -- one of the few major art movements outside New York in the post-World War II period -- Louis was something of a maverick. He worked alone in a small first-floor room in his Northwest Washington house. Only a part-time assistant ever saw him work. Most of his canvases were found stacked in his studio, unstretched and untitled, and wide appreciation of his work came posthumously.

In September, "Morris Louis: The Complete Paintings," a catalogue raisonne' by Diane Upright, will be published. A year later, a retrospective organized by Museum of Modern Art curator John Elderfield -- the first major Louis showing since the '60s -- will open at the MOMA. It will then travel to the Hirshhorn Gallery and Sculpture Garden and the St. Louis Art Museum.

"Louis," said Martha Baer, Christie's contemporary art specialist, assessing his work in market terms, "is not the most fashionable artist, but his work is coming into its own."

Works by Franz Kline, for instance, command more money. A bold untitled black and white abstract executed in 1960 garnered $880,000 in tonight's sale. The 116 1/4-by-79-inch oil on canvas from the estate of Robert Bollt toppled the previous $506,000 record for the artist set in November 1983 at Christie's for "Harleman" (1960). Jesse Philips, a Dayton, Ohio, collector, purchased the Kline.

Sculpture by the late David Smith also has a big following. "The Forest" (1950), a hallmark painted and welded steel work exhibited at the Corcoran in the 1969 Smith retrospective, fetched $264,000.

Even modest-sized works by Dutch-born Willem de Kooning routinely sell for six figures. "Woman, Wind and Window II," a 16 1/4-by-19 3/4-inch enamel and oil on paper mounted on board, brought $495,000. The yellow and black picture, which foreshadowed de Kooning's important "women" series, is illustrated in two well-known monographs on the artist by Thomas Hess and Harold Rosenberg.

Pictures by William Baziotes are coming into their own, too. In May 1981, "Primeval Landscape" (1953) sold for $143,000. Tonight, $209,000 was paid here for "Serpentine" (1961).

Bidding for the Louis started at $100,000. Within two minutes bids raised to the closing hammer price of $350,000. Christie's 10 percent buyer's premium brought the total to $385,000. But the main excitement here tonight was the Kline. Bidding for the untitled abstract began at $400,000.

"I don't expect fireworks," Baer had said before the sale, "but I do expect some action."