One of the more tantalizing what-ifs of Washington's cultural history concerns the 1939 architectural competition for a Smithsonian Gallery of Art on the Mall, won by the Finnish-born father-son team of Eliel and Eero Saarinen.

Radically modern in design and remarkably fresh in concept, the gallery, as we know, was not built. Instead, the winning entry was widely publicized and became for a while a cause ce'le`bre, symbolizing bitter philosophical divisions among architects in the 1930s. Its rejection solidified the capital city's reputation for conservatism in architecture and the arts.

Mina Marefat, an architectural historian at the National Museum of American History, has been investigating the nooks and crannies of the long-ago competition for a year or so, and lately has been giving selected audiences preliminary views of her findings. I first caught her act a couple of months ago in a lecture delivered to the Latrobe Chapter of the Society of Architectural Historians. She makes a persuasive case for the continuing relevance of the competition.

Had it been built, the gallery most certainly would have changed the city's cultural and physical landscape in ways both minor and major. No question, for instance, that the Mall today would have a different look -- the building was designed for the prominent site now home to the Air and Space Museum. Nor is it likely that today's National Museum of American Art would exist -- the proposed gallery would have inherited the materials that form the core of the NMAA's collections.

Being primarily an institution of contemporary American art, the gallery would have formed an ideological, as well as a stylistic, counterweight to the neoclassical National Gallery of Art, John Russell Pope's masterpiece then under construction. Edward C. Bruce, chief of the Treasury Department's fine arts section and the New Deal's most innovative arts bureaucrat, tersely defined the gallery's role as being "dedicated to living artists," in explicit contrast to the "mausoleum for dead masters" across the Mall.

Bruce's conception was both foresighted and far-reaching. He envisioned the institution as "an active, influencing agency." It would collect and display art, to be sure, but it also would serve as a national "clearing house" and educational/research center to stimulate excellence in "contemporary painting, sculpture, architecture, graphic arts, photography, and industrial arts." There's little question that so venturesome an institution -- sort of a cross between the Bauhaus and the Centre Pompidou -- would have had a national impact, and none at all that it would have played a significant part in the development of painting and sculpture in this town.

Most astonishingly and most significantly, perhaps, the materialization of this gallery would have placed the federal government in the forefront of the modern architectural movement. This might or might not have had lasting effects on the government's patronage of architecture, but the very prominence of the building in the nation's symbolic core definitely would have altered history. As it did happen, modern architecture arrived in force a decade later and under corporate sponsorship. Not until 1978, with the opening of I.M. Pei's National Gallery East Building, did the Mall acquire a modern building of the quality promised by the Saarinens' design.

Marefat's interest in the competition was stimulated almost accidentally, as often occurs in scholarly work -- she was researching a different subject when this one seized her attention. The historian's quest has involved a portion of dramatic discovery, as also often is the case: Thanks to a conscientious bureaucrat (name: Andrea Mones O'Hara), Marefat was able to race -- in a Smithsonian car, in a snowstorm, just before Thanksgiving 1989 -- to retrieve a stack of endangered, unidentified competition drawings from the General Services Administration storage facility in Suitland.

These turned out -- yes! -- to be panels submitted by finalists to the two-stage competition held 52 years ago. As a result of this adventure and more conventional academic labors, Marefat so far has located 28 of 30 possible drawings submitted by the 10 finalists. In addition, she unearthed a cache of studies for the building by Paul Cret, the most established and most conservative of the 10.

Altogether these drawings would make up the nucleus of a superb exhibition. The show ought to be done, but is no sure thing; worthy ideas sometimes do get lost in the Smithsonian labyrinth. It helps, however, that Marefat's boss, National Museum of American History Director Roger Kennedy, is himself an architecture aficionado and is enthusiastic about the project.

The Saarinens' design remains relatively well known. The model for it still exists (in storage), and photographs of it reappear from time to time. It has aged into a perfect period piece of the international style -- a fluid, asymmetrical composition of rectangular volumes sheathed in glass and/or stone. But an opportunity to examine this design at leisure, along with some other very beautiful ones, would be both pleasurable and timely. A detailed comparison of the winning design with Cret's scheme, done much in the manner of the stripped classicism he used at the Folger Library and Federal Reserve buildings, would be especially provocative.

In addition, the show and its accompanying research might shed some light on other vexing questions surrounding the competition. Did the Saarinen scheme really have a chance to be built or was it, as supporters often maintained, a "martyr" to Washington conservatism?

What's known is that the design, selected by a jury heavily weighted with modernists sympathetic to Edward Bruce's aims, was destined to arouse the fierce opposition of the Commission of Fine Arts, guardian of the City Beautiful ideals inherited from the McMillan Commission plan of 1901. What is not known are the political intricacies of the struggle -- the whys and wherefores of President Roosevelt's silence on the issue, after his strong support of Bruce on other matters, and of the ambiguous position of Congress, which had funded the competition but pointedly refused to provide construction money.

Such important political details aside, there are fascinating theoretical parallels between then and now. The arguments used both for and against the gallery's design are very like those employed in the debate between modernist and postmodernist architects in the '70s and '80s, with one side insisting on the aesthetic and moral superiority of the new, and the other, with equal conviction, on the necessary precedence of history and tradition.

But then too, such debates were unwisely couched in either/or terms. If modern architects erred greatly in wholesale rejection of existing urban patterns, postmodernists, like the conservatives of yesteryear, vastly underrated the dynamics of change in the contemporary world. Both systems of thought seem closed, self-referential, almost beside the point in evaluating the humaneness -- or lack of it -- in our built environment.

How fine it would have been to have had not the arguments, but the real building on the Mall all these years, a historical landmark unlike any other in the city. And how excellent in its stead to have an exhibition based on the materials Marefat has pulled together. Bring it on.