It's hard to believe that George Bellows' boxing paintings never had all been hung together until the National Gallery assembled them for the exhibition opening Sunday in the East Building.

The show is (excuse it, please) a knockout. Boxing was the heart of Bellows' work, and the dozens of drawings and six bitter oils he executed on "the sweet science" give the measure, for all time, of this dreadfully fascinating sport.

Marking the centennial year of Bellows' birth, the exhibition includes a score of lithographs; many are varied treatments of the same scene and some served as studies for the paintings. The juxtapositions may have the odd effect of somewhat lessening Bellows' reputation as a painter: In general, the lithographs simply are better. This is by no means a denigration of an artist whose use of line, shade, composition and character ranks with that of, say, Daumier and Kollwitz.

The lithographs are endlessly engaging. In "A Knockout" (second state, 1921), perfect in every line, Bellows returned to a scene he had done in pastels and India ink in 1907 as "The Knockout." The earlier work is much more "finished," but the later one shows that he had made a quantum leap in boldness and mastery.

In three studies entitled "Between Rounds," done between 1916 and 1923, Bellows made the merest alterations, mostly in the audiences (which almost dominate his boxing works); each time, he raised the power of the scene by an order of magnitude. In other series he sat too long at his board, diminishing the rawness that demonstrates how, while Bellows loved boxing, he loved truth more.

"Both Members of This Club," with "Stag at Sharkey's" perhaps the most famous of the oils, recently has been cleaned. It has become almost a different picture, and not necessarily a better one. Hanging with them is "Club Night," the infrequently shown companion work from the collection of Mrs. John Hay Whitney. It's the least dramatic but most fully realized of the three.

BELLOWS: THE BOXING PICTURES -- At the National Gallery East Building through January 2.