AMERICAN & EUROPEAN POSTERS ON VIEW: At the Library of Congress Thomas Jefferson Building lower-level gallery, indefinitely.

En route to the Library of Congress reading room even the studious are easily snared by 46 "American and European Posters on View" in the lower-level gallery.

The show's centerpiece is the first 24-sheet billboard ever printed, the 16-by 8-foot "The Horse Fair" by Rosa Bonheur. Horses and trainers move fluidly in vivid colors (hung in a curved alcove for lack of wallspace). It took Bonheur, the first woman animal painter, a year and a half to create the oil of the same size, after disguising herself as a boy and spending days sketching undetected by stable hands and riders around Parisian horse fairs. Then it required five years, the work of 10 artists from the W. J. Morgan Co. of Cleveland, 20 colors and more than 480 stones in the printing process to complete the lithograph. The oil no hangs in the Metropolitan Museum of Art in New York, and the only other lithographic copy is in unknown private hands.

Other workds in the exhibit, representing the library's collection of 70,000 posters, range from refined (a famous Eugenie Buffet poster by Lucien Metivet) to historic (an original linoleum cut by Pablo Picasso for the bullfights in Vallauris to fun (American Railway Express' pretty 1927 ad with the slogan "Southern Foods for Northern Tables"). Classic 1890 French advertisements for carnivals and theater productions mingle with Polish circus posters; political statements about apartheid and the 20th anniversary of the liberation of concentration camps share walls with snappy Milton Glaser and Robert Rauschenberg creations.

We have the acid era to thank for the resurgence of the poster as an art form, poster curator Elena Millie says. "Through the psychedelic movement and the anti-Vietnam War movement, original posters came into being again. They brought back the old circus, film and World War I posters" -- proof that not all posters are best by black light in the haze of a dorm room.

Reproductions of two posters from the show, Emile Bertrand's "Cendrillon -- Musique de J. Massenet" (a Cinderella opera poster) and Paul Helleu's "Ed. Sagot, Estampes & Affiches Illustrees," will go on sale October 1 for $5 and $3, respectively, at the information desk.