MILTON AVERY, whose paintings are so great that even art critics can understand them, finally has been given a room of his own at the National Gallery of Art.

Avery (1885-1965) is described by gallery director J. Carter Brown as "an American original," and that ain't the half of it. Nobody had ever painted like Avery before, and no one has succeeded in painting like him since, although many an art student has tried. Avery hung out with the abstract expressionists of the New York School, but he didn't paint like them. He wasn't a realist either. He was just Milton Avery, a man whose landscapes make you glad he lived, and that you lived to see them.

Avery was born into a working-class family in upstate New York and went to work in a factory at the age of 16 to help put food on the table. This dreary existence continued for much of his early life, but the young man never ceased looking dreamily out the window. While working the day shift on an assembly line in Hartford, Conn., he enrolled in night classes at the Connecticut League of Art Students.

Whatever his instructors may have taught Avery about materials and techniques, the vision he brought to his art was utterly individual. His first public exhibition was at Hartford's Wadsworth Atheneum at the age of 20, but twenty years more would pass before Avery was able to move to New York City and paint full time.

This city boy/factory drudge somehow held and matured a vision of nature so rich and realized that you'd think he was raised by the Muses, on the shores of Walden Pond. Avery's landscapes are really dreamscapes, ideals distilled into color-defined shapes that permit the viewer to share Avery's vision to a depth unmatched by any of his contemporaries.

His work in fact is the very definition of abstract expressionism, but stands apart because others have lacked the genius required to follow his lead. Almost alone among modern artists, Avery recognized that it is not the duty of the viewer to understand the artist's inner vision; it is the duty of the artist to make the viewer understand. That's what they get paid for.

The current exhibition is sort of a tryout. Curators Jeremy Strick and Marla Prather have chosen six oils that embrace the span of Avery's most limpid and powerful period: "White Sea" (1947), "Two Women" (1950), "Advancing Sea" (1953), "Sunset Sea" (1958), "Sand Dunes and Yellow Sky" (1959) and "Mountain and Meadow" (1960). They'll be on view until mid-April and then again in October; the shuffling has to do with the gallery's 50th anniversary celebration and acquisition plans.

The Averys are installed in concourse gallery No. 6, replacing a New York School show, and the placement is devastating to the works in the adjacent galleries. Even devotees of Richard Diebenkorn and Mark Rothko may find their paintings thin and sterile beside Avery's ethereal evocations of real-world joys. MILTON AVERY:

Six Paintings -- Through April 14, and again beginning Oct. 1, in the East Building, National Gallery of Art. Open 10 to 5 Monday through Saturday and 11 to 6 Sundays.