The building dwarfs the mind; more literally, it dwarfs the basketball game echoing from one end where employees bounce away a lunch break. Faced with the vastness of this 19th-century Pension Building, the 20th century's grandiose Hyattization of America seems stale fare.
That, of course, is placing things in perspective. And if Montgomery Meigs's Pension Building helps us to do so by its very existence, that is only suitable. ''The building just says 'building,' '' says Bates Lowry. By doing so, it symbolizes its formal new mission: ''to commemorate and encourage the American building arts.''
A year ago, this vast space was put to the service of the art it so hugely represents. In the fall of 1980, the federal government mandated the creation of a National Museum of the Building Arts in these quarters.
Since then Lowry, director of the so-called ''Building Building,'' has overseen the restoration of the courtyard fountain while putting to rest the myths about the horses stabled on the fourth floor. He has supervised both the new physical life ($2 million in repairs to the roof alone) and the intellectual one (defining and organizing the goals of the institution).
Above all, the energetic director has underscored its link to a constituency to which the phrase ''built environment'' may be as exotic as the 16-story Corinthian columns that loom over the museum's courtyard, the size of a football field.
''You walk in here and you just think 'building,' '' Lowry says as he emphasizes the expansive nature of the program in line with the expansive space.''
''Not just architecture, but everything,'' he asserts. ''Just the height of it makes you think of the draftsmen and the workmen. I never want to fill it up.
''I don't want it to be an attic filled with cranes.''
Instead, the phalanx of chambers that march around the glorious inside-outside courtyard will become exhibit rooms and offices for a staff that should expand from today's 10 full- and part-timers and 30 to 40 volunteers.
To do so, this fledgling institution obviously needs to raise funds - no easy task when so many older programs have been ray-gunned into inactivity.
Lowry, a large mustached man whose acquaintanceship in the museum field is as far-reaching as his long stride, seems to possess the verve, plus the new fund-raiser, John Callahan, to achieve what Lowry calls ''a long education process.''
Part of that process has already begun. This past summer, for instance, the museum turned out Blueprints, its attractive newspaper/newsletter.
Featuring a centerfold drawing of a design from the Philadelphia Centennial, the bulletin speaks about the museum's own goals (''to encourage the public to take part in the ongoing debate over what relationship our society should establish between the built and natural environments'') and word on events across the country, from Michael Graves's civic building for Portland, Ore., to reviews of books and notes on traveling exhibitions.
Currently, such shows start in one city, summoning the labor and imagination of their organizers. Then they fold. The National Building Museum can give space to extend the useful life.
The museum will open its own exhibition with ''America Builds Abroad,'' models and tapes on the embassies created by the United States - America's face to the world. It has tentatively scheduled shows from other sources: the Museum of Modern Art's Neutra exhibition, a view of art deco movie theaters from the University of Minnesota Art Gallery, and, in 1985, a show of ''Cranbrook Academy of Art: the Emergence of Modern American Design.''
In a more active vein, the national building museum has cosponsored a contest on ''Saving Energy in Historic American Buildings,'' with the Association of Collegiate Schools of Architecture.
As director Lowry walks through the brontosaurusian structure, he is also quick to point out the 19th century's ecologically conscious attitute, which is evident in his own building.
Once upon a time, 1,500 bureaucrats dispensed pensions from the mammoth structure; its 100-by-300-foot dimensions allowed the penetration of light and air while providing ceremonial space for the inaugural balls of presidents from Cleveland to Carter.
Information on that and other material pertinent to the building industry will sit in a data bank centered in the National Museum of the Building Arts.
A constituency that ranges from bricklayers to architectural historians, the Society of Experimental Stress Analysis to the Victorian Society in America, would have access to such material.
Such a disparate group of supporters will certainly disagree on the role of the museum that is the focal point for all the building arts, high and low, facade to plumber. Once the museum has taken the step beyond today's consensus and foundation building, it will have to respond to hod-carriers and quill-pen flourishers.
The balance between its service to scholars and its aim to educate the public at large will promote some controversy, too. (The current emphasis on the wonderful world of video, for one example, seems a bit diaphanous to this viewer - pipe dreams to capture the six hours of daily TV consumption.)
How not to give offense to some 29 professional organizations supporting the enterprise, yet promote a critical eye toward the built environment?
Nonetheless, ''working with mirrors,'' in one observer's words, the director has brought the national building museum from idea to execution. He has kept his eyes open to the largest aspects of design while producing a novel institution, America's first architecture museum.
The aim is to create a place where ''things having to do with building, not just architecture, can develop,'' Alan Fern of the Library of Congress, a board member, adds.
''Urban studies, social psychology, public housing - I think the direction is fundamentally to educate the public, to bring about a stronger, sharper awareness of architecture in the broadest sense.''
Now that America has come of an age to create an institution to do so, it is only fitting that its attitude, like its three-ring-circus Pension Building space, be large enough to hold a cast of thousands.