Birds may be freewheeling beings, but bird painters are not.

Bird painters take the greatest pains and use the smallest brushes to insure that each beak they paint, each feather's barb and barbule, each claw and beady eye, is portrayed just so.

Bird painters never wing it. Their seriousness is stunning. Hail to thee, bird painters -- blithe thou never wert.

The pictures they produce in such astounding numbers are astoundingly conventional. "Birds: Works from the 1979 Annual Exhibition of Art Depicting Birds," which goes on view today at the National Collection of Fine Arts, is an exhibition both admirable and awful. The craftsmanship is splendid, but the sameness of these pictures begins to numb the mind.

You'd think that whittlers of decoys would tire of carving ducks, that painters who paint geese in flight would grow sick of the honkers. Yet one leaves this exhibition -- and many others like it -- awed by the devotion of those who portray birds.

There is about their art something slightly sacred. The painting of birds -- like the spinning of a prayer wheel, the saying of the rosary or the muttering of mantras -- is an act of tedious prayer.

Painters might not know it, but multiple and constant are the muses that they serve. The goddess of the earth is sensed in every bowl of fruit in every painted still life; the goddess of the woodlands graces every landscape; in another aspect she rules every seascape, for waves and boats are hers. We serve her with the fruits and flowers we center on our tables, and we also summon her with images of birds.

Birds are grand to watch, but lovable they're not. They stink, if truth be told; they peck at one another, and they take their wondrous flights on automatic pilot. I did once meet an owl I liked, but he was an exception. Our feathered friends are beautiful, but they are not friendly. Their scaly legs are sinister. Beneath their lovely plumage they resemble snakes with wings.

There are thousands of bird artists. Hundreds submit pictures to the regular exhibitions arranged by Ducks Unlimited. Hundreds more appear to dwell on Maryland's Eastern Shore. There is scarcely a village in America that does not boast an artist who paints weathered barns in Andrew Wyeth's style. Similarly numerous are the people who paint birds.

A number have grown famous -- J. J. Audubon, for instance. Others have grown rich -- Walt Disney, for example, or the late Edward Marshall Boehm, who made a fortune mass-producing his hand-painted porcelain birds. Women not so long ago wore stuffed birds on their hats. Robin Hood wore feathers. In Richard Nixon's Oval Office there were birds by Boehm.

The 47 bird works in the present show were drawn from an exhibit organized last year by the Leigh Yawkey Woodson Art Museum of Wausau, Wis. The painters, printmakers and carvers represented here are colleagues of a sort, belong to the same flock, though the works they have produced are not all alike.

Some of them succumb to Disney dramatismo: Peter Markham Scott sends his Canada geese flying toward the sunset; the large owl of Kurt Pendleton looks at us and winks, and Kenneth Carlson's trumpeters fly in hokey splendor among purple mountain majesties and white swirling mists. Bird painters, on the whole, do not fear the sentimental. It is refreshing then to see Donald L. Malick's eagle -- with feathers in its beak and a hornbill, partly disembowled, impaled on its talons. Robert Bateman's handsome "Gentoo Penguins and Whale Bones" is comparably instructive. These two works remind us that birds do defecate and kill.

Though most of the bird artists here are meticulous precisionists, a few of them do use loose, suggestive brushstrokes. Manfred Schatz's mallards are not in perfect focus, nor is the golden eagle painted by Guy Coheleach. Because they are good painters, their brushwork appears daring, particularly in the context of the tightness of this show. Arthur B. Singer's looseness appears unintentional. He paints muddy trees.

Only rarely do these bird works recall other sorts of painting. One sees too much of Wyeth in Burton E. Moore Jr's painting of a pitted decoy on a box of shotgun shells, but it's nice at the same time to see that he has looked at pictures that are not bird art. Something of the old European masters has touched the work of Raymond Ching, Oriental masters have similarly instructed Heather Dieter Bartmann, and surrealism haunts William Zimmerman's painting of a sharp-shinned hawk.

These artists know their subjects. All of them, it's clear, have paid close attention to the anatomy, the plumage, the flight patterns of birds. Yet only at first glimpse do these wellmade pictures and admirable carvings seem to honor freedom. So formal are its rules, so rigid its conventions, this kind of art seems caged. The exhibition closes May 6.