"Recent Trends in Collecting: Twentieth-Century Painting and Sculpture from the National Museum of American Art," which opened there yesterday, is a quirky exhibition, full of footnotes and surprises. While some museums strive to build "masterpiece" collections, Harry Rand, the curator under whose regime these 130 objects were acquired, had something else in mind.

Harry Rand likes oddities as much as he likes masterworks, objects out of fashion as much as those in vogue. A kind of reverse snobbery hovers around his show. For every famous artist in it -- Edward Hopper, Morris Louis, Franz Kline, Kenneth Noland, Joseph Cornell, Mark Rothko, Rockwell Kent -- there are others few have heard of. The three Pollocks on display are not by Jackson Pollock, but by his brother, Charles. Also unexpected are two awkward pictures here by the late Jennings Tofel (1891-1959), "a dwarf and hunchback, a foreigner, a difficult modernist, a Jew, a man without the gift of personality," who, so Rand contends, is "most undeservedly obscure." Rand sees his museum as a "museum of record." One truth his show records is the confusing messiness of the history of art.

The National Museum of American Art (formerly the National Collection of Fine Arts) is not a rich museum. Its acquisition budget is only $200,000 a year. A few pictures in Rand's show may be worth hundreds of thousands of dollars (the large Louis, for example, the Hopper or the Kline) but here they are surrounded by others that might sell for only a few hundred. The weakest objects here -- that little David Smith, that blotchy Milton Resnik -- are very weak indeed. Rand compares building a museum collection to constructing a fine clock with parts that come to hand. His clock makes eerie noises, it squeaks and honks and rattles, but it does keep time.

Rand's show is held together by interlocking themes:

* One is early oddities. Rand writes that his museum "actively collects the early production of artists who came late to fame," and a number of such works, most by local painters, are included in his show. Jacob Kainen, for example, is represented here by pictures dated 1938, 1941, 1951, 1961 and 1978. That 20-foot wide "unfurled" Morris Louis, dated 1960, is revealingly accompanied by an early, messy Louis of the sort the painter preferred to destroy. A 1964 Kenneth Noland "chevron" (which came to the museum, as did many objects here, from the collection of Washington's Vincent Melzac collection) is similarly installed beside a little Klee-like Noland that the artist had completed a dozen years before. Other local painters -- Alma Thomas, Thomas Downing, Howard Mehring -- are also represented by pictures they produced before their signature styles firmed.

* A second theme is "teachers." Artists now remembered not only for their art but also for what they taught to others are well-represented here. These include Kainen, Morris Kantor (a New York teacher Rand describes as "fabulously important"), Ed McGowin and Tom Downing (who both taught here at the Corcoran), Stanley William Hayter, and John Graham of New York. (Rand describes Graham as "one of the central figures in American art. A friend to Stuart Davis, Lee Krasner, Milton Avery, Arshile Gorky and Jacob Kainen, Graham 'discovered' Jackson Pollock, helped to interest David Smith in sculpture . . . and served as a liaison between the artists of Paris and New York.")

* A third theme is the monograph. A number of these artists -- Kantor, Kainen, Graham and Cornell, among them -- are represented in some depth.

* "American scene" pictures, many of them urban views from the 1920s, the '30s and the '40s, also lend some order to this varied show. Painters John R. Grabach and Xavier J. Barile, neither of them famous, are represented here by pictures of New York. Sculptor Chaim Gross displays a plaster bas relief of riveters at work. A rather somber painting of less-than-happy coalminers by one Maurice Kish, a man Rand says has been granted his own museum in Leningrad, also is included. Near it is a first-rate Reginald Marsh, "Locomotives, Jersey City" (1934). Because Franz Kline is represented not only by a large black-and-white abstraction of 1961, but also by another locomotive painting done 20 years before, the gritty and partially political American-scene paintings here function as a thread that leads the viewer through the show.

Rand seems to like surprises. Two very slightly known painters from this city, Jozef Pielage (who is represented by a lovely garden scene from 1969) and Martha Moffett Bache' (who shows a wartime market scene from 1942) are among the far-from-famous artists he's included. His curious exhibition, though it is by no means beautiful throughout, does evoke much thought.

Rand's attitude to collecting seems to be in harmony with that of Joshua Taylor, the museum's late director. "Quality," wrote Taylor, "comes in many guises . . . It is better to be historically wrong than emotionally crippled. History can change."

A second exhibition of recent acquisitions also is on view at the museum. This pretty, thoughtful show of prints, drawings and watercolors, includes at least one masterpiece -- a delicate chalk portrait of Walt Whitman by Thomas Wilmer Dewing from 1875. Such masterworks may well distort our reading of art history, but there is something to be said for objects of such quality: They sure do please the eye. Rand's exhibit closes March 28.