Not one, but three exhibits of the work of Milton Avery open here today.

The choice oils at the Phillips Collection stress the later stages of his long career (he was born in 1893 and died in 1965); the Lunn Gallery, 3243 P St. NW, is showing watercolors and drawings, as well as a few oils; the Middendorf Gallery, 2014 P St. NW, is exhibiting the prints. There are many reasons why these shows shoud be seen.

Avery is accessible. His pompous, klutzy birds, the seashore that he loved, his daughter and his wife, are painted with such obvious affection that the viewer sees at once that Avery, the master, had fun painting pictures. His art is witty, spare, and easy, and it does not show off. Avery is an ally of the weekend painter, the happy amateur.

He is historically important because his paintings bring to mind France, New England and New York, and link Winslow Homer and Ryder, poets of the seashore, to the "tougher" colorfield painters of our day. "White Wave" at the Phillips, or the picture now at Lunn's in which the horizontal line cutting the sea-field is a speedboat's wake, show how he approached, and how he kept away from "pure" color painting . Nature was his muse, and he thought abstract art "too easy."

Avery is a colorist ofhuge sophistication. No wonder Duncan Phillips liked his work so well. His hues are never flat, they shimmer and they twinkle, but he used simple cut-out shapes. This shape is a dress, that shape is the sky. He used complex techniques, overpainting, underpainting, the brush, the handle of the brush, the razor and the rag, but his effort rarely shows.HIs pictures are serene, with perfect color pitch.

The quiet magic of his art is known well in this century. No other major 20th-century figure has been shown in Washington so often.

The art of Milton Avery has been skillfully promoted here by Sally Avery, the artist's widow. His pictures, since his death, have been placed on view here in three commercial galleries and in three museums. All of these exhibits were orchestrated by Sally Avery.

Duncan Phillips was the first Washington collector to buy a work by Avery (an oil called "The Gallop," dated 1929.) Between 1943 and 1965, the Phillips bought 11 more. And it has given Avery five solo shows, in 1943, 1944, 1953, 1965 and 1977. In 1969, with Sally Avery's cooperation, Adelyn Breeskin of the National Collection of Fine Arts organized an Avery Retrospective. And the Corcoran has shown all of the artist's prints.

Works by Milton Avery have also been on sale here. The late Esther Stuttman, a family friend was the first local dealer to show the artist's work. In the last years of her life, she worked with Harry Lunn (who wrote, and also paid for , the Corcoran's print catalog), and Lunn thereafter organized his own Avery show. His gallery is so busy now (his art sales last year totaled more than $1 million; that Lunn, with Sally's concurrence has passed the local Avery print concession to Chris Meddendori. The prints are there for sale now. Lunn does not get a cut.

"I wanted exposure," says Sally Avery. "A lot of artists can't stand exposure, but the more you see of Milton's work the more you fall in love. I encouraged shows.You throw bread on the water, and it comes back as cake."

The Averys were poor once. Sally Avery supported them by drawing illustrations for The New York Times. They were poor in 1940 when Joseph Hirshhorn bought from Avery a batch of early paintings (she says he paid a pittance), and sometimes in the '50s, the artist's sales totaled only $50 a year. When he died in 1965, she might have sold off his best paintings, but that's not the way she works.

"I had faith," she says, "I knew his reputation would eventually zoom." She held back his biggest paintings, though she often loaned them, and she began arranging sales of his monotypes and prints. "You have to keep the market alive," she says. The least expensive Avery prints now cost $150. The most expensive oils sell, if she agrees, for more than $200,000.

By insuring a supply of dealers and museum shows, viewers and collectors, Sally Avery has helped make Milton Avery a star.

"Avery was a great poet-inventor who invented sonorities never seen nor heard before," said his friend, Mark Rothko, in 1965. "From these we have learned much and will learn more for a long time to come." If one considers what has happened to the paintings that Mark Rothko left his heirs, one sees that there is also much that can be learned from the way that Sally Avery has promoted - and protected - her late husband's art.

The Sander Gallery, 2604 Connecticut Ave. NW, is showing the extraordinary photograph of Andre Kertesz who was born in 1894 and who is still taking pictures. Most commercial photo shows are busy and chaotic, mere catalogs of images. All the pictures here support all the others. This show has a theme. In every photograph on view - some were made in 1918, some in 1976 - Kertesz shows a bird.

A single pigeon flies against a New York sky, in a Paris pond swans paddle, a chicken made of glass sits upon a windowsill, on a market counter is a pile of dead ducks.

Kertesz has for years been acknowledged as a master. His photos never bore, they do not rely on tricks, his photographic style is determined not by habit, preconception, but by what he sees. This exemplary show closes June 4.

"Accessible Arts," an undistinguished photo exhibition which was previewed yesterday at the National Gallery of Arts, suffers from commercialism, bland stock-brochure design, and general poor taste. The firm that paid the bills makes patent drugs, and lots of money, and does not need to have four of its ads posted for the tourists on the Gallery's main floor. I accept the show's contention - the handicapped should have access to the arts and ramps for wheelchairs and labels they can read - But the dozen photo panels installed at the Gallery did not much help their cause.