FOR A MOMENT in the middle of the 19th century, the American frontier lay on the west bank of the Mississippi, and artist George Caleb Bingham was there to capture it for all time.

Born in Virginia, Bingham was carried along with his family in the westward tide. During his boyhood in Missouri he came to know -- and, plainly, to love -- the American types he later would teach himself to draw and paint: the dirt farmer, the country squire, the stump-jumping politician, the Bible-thumping preacher, the backwoods judge, the larger-than-life boatmen who plied the mighty Father of Waters.

These people were his contemporaries, his friends and neighbors, but Bingham rendered them with a prescient historicism, as though he were looking back to some distant but clearly remembered time. Idealized and even rather romanticized, they stand as individual characters who collectively represent the American character.

Washington museum visitors are being treated to a movable feast of Bingham's works this summer, although it is the visitors and not the works that will do the moving. A gorgeous exhibition of 55 of Bingham's drawings and 29 of his paintings, assembled by the St. Louis Art Museum, has been split between the National Museum of American Art and the National Gallery of Art. Unfortunately the shows will overlap for only a month, from mid-July to mid-August.

This curious, inconvenient and artistically ridiculous situation comes from a decision by National Gallery curators to exhibit only the paintings, beginning July 15. American Art's curators snapped up the orphaned drawings, which go on display this Friday.

American Art has done Washingtonians a great service by rescuing the drawings, which all are studies done in preparation for the paintings. Bingham seems never to have done master sketches for his paintings, but to have assembled them from figures drawn in such detail that they are fine, finished, stand-alone works. Sometimes he actually traced the drawings onto the prepared canvas.

Once you've seen the drawings, it'll be torture to have to wait several weeks for the paintings. One consolation is that we'll be able to shuttle between the shows from Gallery Place to Archives on Metro's Yellow Line.