"Ruins and Revivals: The Architecture of Urban Devastation" is an exhibition of photographs on view at the American Institute of Architects headquarters. It concerns the slums in American inner cities, and although the material is hauntingly familiar, the exhibition is at once sobering and depressing.

"The Center for Innovative Technology: A National Competition" is a voluminous show of entries at the National Building Museum. The competition was designed to stimulate "the poetic use of technology in the creation of architecture," and the submissions, unsurprisingly, are optimistic to a fault.

Although coincidental, the juxtaposition is provocative.

Ruins are, by necessity, the featured elements in "Ruins and Revivals," which consists of photographs taken between 1978 and 1983 by sociologist Camilo Vergara along with panels of text written by Vergara and social historian Kenneth T. Jackson. Vergara took pictures in more than a dozen cities, but he focused on the South Bronx and slums of similar bleakness in Newark, Camden, N. J., Chicago and Boston.

The show documents the process of decay in American slums and demonstrates important changes in their character. Overcrowding and its attendant ills have been replaced by institutional abandonment and physical, as well as psychological, isolation. This makes a unique, hostile, somewhat surreal new form of cityscape -- placeless places where rubble-strewn vacant lots, burned-out buildings, boarded-up windows and abandoned "citadels" (insurance companies, banks, once well-to-do churches) compete for attention with structures still in use.

In this environment "revival" is a relative term. Survival is perhaps the better word. It is often accomplished by defensive architectural alterations (store windows sealed with cinder blocks, businesses and yards surrounded by high chain-link fences), by gritty adaptations (transient store-front churches, block associations of hardy homeowners) and, occasionally, by poetic transformations, such as the ark being built from debris on a vacant lot in Newark by Kea, a church caretaker.

The exhibition makes clear a fact that most of us would rather forget: The new slum landscape is as much a part of the contemporary American scene as the spreading suburb, the commercial strip, the high-rise office cluster and the upscale retail center. The show also makes clear, implicitly, the lack of substantial policies, private or public, to truly revive these forlorn areas, and it emphasizes the tremendous costs in human terms of such abandonment.

By contrast, the CIT exhibition epitomizes much that is ebullient and creative in the American economy. The Center for Innovative Technology is an imaginative, state-supported effort to capitalize on the research capacities of leading Virginia universities by making them available to private industry. The aim is to lure technological firms to the already booming northern section of the state.

It is, in other words, a down-to-earth enterprise designed to produce immediate and long-term economic growth. The dreamy spirit of the competition is something else again, and can be summed up by a definition supplied by one of the entrants: The center, it says, is to be "a vessel for the cutting edge of man's aspirations as we approach the 21st century."

The exhibition, ingeniously installed between the ground floor columns of the National Building Museum, presents an unwieldy amount of information. There are 240 panels, each presenting aspects of a design solution in some detail. Fifteen winning entries (five each in first-, second- and third-place categories) are marked with red dots, and even should one examine just these boards (three per entry for a total of 45), one would be unable to predict what the actual building will look like -- the competition was strictly for ideas from which the client and the actual architect (yet to be selected) can pick and choose. One leaves the exhibition with a cumulative impression of having had a heady, though not entirely likable, look into a high-tech architectural future. Very few of the entrants were able to avoid the temptation to overdesign and overbuild, and very few seemed to have clear ideas about the actual needs of such an institution. To be sure, they were not given much guidance by the competition documents, which were strong on enthusiastic, vague generalities and weak on details.

The chief challenges competitors had to face were two: how to provide an emphatic and appropriately technological image for quite a small building (the center will be constructed in several phases, with the first comprising about 20,000 square feet for meetings and offices), and how best to treat a beautiful wooded site straddling the border between Fairfax and Loudoun counties near Dulles Airport.

Not surprisingly, many of the entrants, including almost all of the prize winners, responded to the first requirement by locating a vertical element on a prominent spot. Usually this element took the form of a communications tower of some sort, either free-standing or part of a building. This seems fitting, although the tower's final form obviously would be determined mainly by the center's real communications needs.

Responses to the second challenge varied immensely. In some entries, buildings were scattered like buckshot, in others they were arranged in serpentine or circular or pinwheel patterns, and in others they virtually obliterated the site. Perhaps the most promising idea, again apparent in quite a few of the winning entries, was to arrange the buildings on parallel axes focusing on a central element (usually a tower or, in one exceptional entry, twin beacon-like towers).

This is a fitting notion in a state whose primary architectural accomplishment is Jefferson's Lawn at the University of Virginia. Also, it seems to yield a harmonious relationship between buildings and site, and to answer several other clear requirements, including the need for flexible work spaces, communal rooms, and orderly expansion. We shall see what the real architect comes up with.

The CIT show continues through June 9 at the National Building Museum, while "Ruins and Revivals" will be on view through June 28 at the AIA headquarters.