"This is not an exhibition, it is a life," said painter Philip Guston when his retrospective opened at the San Francisco Museum of Modern Art last May.

His words proved to be prophetic. A few weeks later, at 66, Guston was dead of a heart attack. The exhibition, however, opened last night at the Corcoran. And it does represent an extraordinary life that even art mavens may know little about.

Guston's good friends Jackson Pollock (with whom he was expelled from Manual Arts High School in Los Angeles at age 15) and Willem de Kooning and Franz Kline are all well-remembered as major abstract expressionist painters. But Guston's involvement with them went out of focus -- and his art out of the public eyes -- sometime in the '60s. This exhibition explains a lot about his high independence, his impatience with a style once mastered, his need to move on. It also suggests that his talent was far larger than most have realized.

Stylistically, Guston had three distinct incarnations, and this show reflects them. At age 25, this son of Polish immigrants was well-established as a semi-abstract mural painter, influenced by Picasso, the surrealism of De Chrico and the realism of Mexican mural painter Siqueiros, with whom he worked in Mexico.

In 1935, at the behest of Pollock, Guston moved to New York and did several major commissions for the mural section of the WPA. He had also begun to make easel paintings, including several dealing with the plight of American blacks beset by the Ku Klux Klan -- these paintings were destroyed by gunfire during a police raid. A drawing made at age 17 stands in for the ruined paintings here, though some paintings from the '40s -- figurative allegories dealing with the impact of war upon children -- suggest his persistent social concerns.

In 1949 Guston was pushing toward abstraction of his firms, becoming less interested in subject matter than in the act of painting itself. By 1952, when he showed with de Kooning and Kline at the Egan Gallery, he was a full-fledged abstractionist. A room of paintings here shows the evolution of his abstract style from rather delicate tentative beginnings to its full blossoming in the late '50s and early '60s. Rich, thickly impastoed works like "Beggar's Joys" and the dramatic hommage "To Fellini" are but two among many beautiful and increasingly bold paintings.

In 1963, at age 50, Guston was given the first retrospective ever mounted by the new Guggenheim Museum in New York. His reputation equaled the best of the abstract expressionists.

But in 1966, with a Ford Foundation grant, the first of two Guggenheims, and the Prix de Rome under his belt, he ceased painting for three years, and after an 18-month dalliance in Florida, returned to Musa, his wife. He began to develop, in scores of drawings, the new iconography of forms that would dominate his late work. His hooded Klan figures emerged like ghosts from his own past -- but now as amiable, cartoony symbols that came to represent the artist himself. There were also highly simplified, naive-looking studies of common objects he'd dealt with in the past: shoes, clocks, paper hats, chimneys and upside-down legs -- many of them clumsily painted in an effort to get the ideas worked out.

In 1970, Marlborough Gallery, unfortunately prematurely, showed the new cycle of work, and The New York Times critic howled. Guston left New York for good and moved to Woodstock, where he created the late cycle of work that fills the last three galleries. The paintings become stronger and increasingly autobiographical, and are among the finest he ever made. Guston ate a lot, smoked a lot and drank a lot. Many of the works, including "Bad Habits," show the artist half submerged in these images, but with a sense of humor. The last painting in the show is a wagon wheel mired down in the mud.

This exhibtion -- the Corcoran's big summer event -- continues through Sept. 9.