As kids we used to gallop home from cowboy movies on imaginary ponies. We strutted in our jeans and hung cap guns by our beds. So somewhere in our secret selves all of us are Westerners, fearless and outdoorsy, lean and free and proud.

"The First Western States Biennial" - although a group show full of modern art - conjures just such fancies. It goes on view today at the National Collection of Fine Arts, and is an easy show to like.

It is witty and wide open. It stars sharp-eyed painters, adventurers, loners and tellers of tall tales. The finest objects here bust right through the tacky. They are as well made and flamboyant as hand-tooled snakeskin boots.

Twenty-eight artists, not many of them were selected by committee for the show. Some hail form Baltimore, Brooklyn, Boston or Chicago, but all of them now live in the 10 states west of Texas, or Alaska or Hawaii. No area so enormous should be called a region, but there is something regional - a welcoming spirit, a willingness to please - in this new western art.

New York art, in general, is a bit off-puting, shadowed, anguished, grim. Chicago's art is feaky; Washington's is prim. The Western objects are wholly different. They do not dare the viewer; they entice him. Though their freedom is unfettered, they will not shock. Their jokes and stories entertain; their colors suggest sunlight.

Luis A. Jimenez Jr. of Roswell, N.M., a greatly gifted sculptor who appears to know no embarassment or fear, made the extraordinary statue - of painted gold-flecked plastic - that dominates the show.

His cowboy, riding a bright-blue bucking pony, wrangles simultaneously with a red-eyed longhorn cow and a hundred old cliches. Jimenez gleefully alludes to rattlesnakes and gunfights, the movies of John Ford, mass-produced Boehm birds, the glitter of Las Vegas and the bronco-busting bronzes that Frederick Remington made for Edwardian parlors when the Wild West was new. He who hesitates is lost, and Jimenez crashes through.

California's William Wiley, the best-known artist here, is comparably fearless, Wiley adores puns. From across the room, his "The World at Large" with its yellow square centered in a gray one seems to be a pun on Josef Albers - until one discovers the Hollywood phantasmagoria that the wily artist has drawn in gray on gray. Sailboats and gun molls, rocketships and top hats and a hundred other images, among them a self-protrait, flicker in his fog.

New Mexico's Paul Sarkisian may well be the most skillfull trompe l'oeil painter now alive. There is something of Robert Rauschenberg in the eastern elegance of Sarkisian's large collages - except that they are not collages. Rauschenberg glues his papers down; Sarkisian doesn't. There is magic in his airbrush. His squashed Ritz Cracker boxes, his feed bags and paper tapes, some of them translucent, are all painted in by hand.

Frank Anthony Smith of Salt Lake City applies paint for more loosely, but also fools the eye. His "Casa delas Culebras" (which has been given to the National Collection by the Ford Foundation) seems a cluttered field of paper scraps, paint spills wooden dowels, string - and hummingbirds - all painted in by hand.

Another meticulous realist, Merrill Mahaffey of Phoenix (whose "Toroweap Sandstone" has been given to the NCFA by the Dayton Hudson Foundation), seems, within such company, a somewhat bland technician. He shows us red southwestern rock. Other artists here delight us with their dreams.

Montana's John E. Buck, who whittles, recalls in his "Aloha" Marc Antony, Picasso, the Pyramids of Egypt and Cleopatra's asp. His work is nonetheless western in its wackiness. Alaska's Daniel De Roux has set tooth-brushes, dogs, ducks and a wedge of blueberry pie dancing in his cartoony composition," All the Joys That a Good Home Brings." The porcelains of Nevada's Chris Unterseher, though just as heartfelt, are less fantastic. Unterseher hymns Noel Boggs, Speedy West, Billy Bowman and other masters of the pedal steel guitar.

A number of the objects here look out of place at first glimpse, as if they might have been made anywhere. The planar sculpture of Seattle's Robert Maki, the layered papers of Arizona's Beth Amers Swartz, and the steel-and-chalk-line composition of Wyoming's John Van Alstine do not stand a chance against this show's exuberance. They have the leaden look of art-school art.

It is not that they're "abstract." Seattle's Francis M. Celentano makes stripe paintings that glow, Denver's Vance Kirkland suggest, with dots of color, huge, expanding galaxies, and New Mexico's Jean Promutico summons in her painting the star-bright western sky.

The chevrons and huge burshstrokes of Portland's Lucinda Parker are at least half-familiar, but she paints with verve. Boulder's Jerry Kunkel is a shaman of a sculptor. He seems to have collected sticks and stones and colors for some private magic rite.

Not so many years ago, Manhattan, Los Angeles and a few other cities ruled the U.S. art scene, or at least the standard repertory seen in our museums. That hegemony is cracking. Morris Graves, Andrew Dasburg, Helen Lundeberg, and the ubiquituous Georgia O'Keeffe, who have been included here as "honored invitees," suggest that the domination began fading long ago.

"The First Western States Biennial Exhibition" was organized by the Western States Arts Foundation. Funding was provided by the National Endowment for the Arts, the Dayton Hudson Foundation and Phillip Morris Inc. (which has purchased for the NCFA "Man on Fire," a sculpture by Jiminez). The show will travel to San Francisco and Seattle after closing here on Sept. 3. CAPTION: Picture, Luis A. Jimenez Jr.'s "Progress: Part II"; by Harry Naltchayan