Anyone who stumbles unprepared into "Speaking a New Classicism: American Architecture Now" at the National Museum of American Art is in for a big, potentially disorienting, surprise.

Where am I? Who's on first base? Where is first base? What century is this, anyway? These are questions that might occur to a viewer who hasn't looked at an architectural magazine for the past couple of years. The show is a veritable time-warped hothouse of moldings, colors, ornaments, decorations, columns and classical orders--more or less precisely rendered, or turned inside out and upside down.

The show is preposterously titled, of course, in the nature of polemical enterprises. Far from representing the state of American architecture now, the exhibit presents a limited survey of recent plans, drawings, models and artifacts from a limited, if extraordinarily creative, segment of current architectural practice.

And even then the picture it provides is far from clear: The show teems with architectural ideas, but together they do not add up to a definition of what "new classicism" might be. "Mumbling or stammering the new classicism" is what one of the participating architects suggested as a more accurate title for the exhibit.

Classic revivals are nothing new in architecture. It has been argued that, starting with the Greeks, classicism is the mainstream of the art in Western cultures, with exceptional interruptions (the Gothic, the Modern) to prove the rule. What is presented in this exhibition, however, is something else--not so much a revival of classicism as a renewed interest in the malleable possibilities of the classical orders, and in the potentialities of history itself. Above all, what unites the disparate endeavors in the exhibition is a rejection of the central modernist idea that to deny history and start anew is both necessary and desirable.

Three quite different, if often overlapping, attitudes emerge from the show. First, there are the architects, a distinct minority, who practice their classicism more or less straight. Using "traditional elements of architecture in a traditional way," for instance, John Blatteau conceived an addition to the Bayonne (N.J.) Hospital that could have been designed by a skillful American Beaux-Arts practitioner in the early 1900s.

Similarly, Philip Johnson, the International Styler turned brilliant eclectic, designed three buildings for the Sugarland Office Park near Houston that have a deadpan look of absolute ordinariness in their low massing, brick fac,ades and minimal classical motifs such as slightly projecting pediments with ocular windows. Johnson said he borrowed the design from the works of Karl Friedrich Schinkel, the great Prussian classicist of the early 19th century, although many of the elements were ordered from today's architectural catalogues.

The strategy of straight revivalism is hard to object to on a piece-by-piece basis. Johnson justifiably says his design "looks almost elegant and, incidentally, just as cheap" compared with the "thousands of boring glass cubes of Houston." Still, it hardly represents the wave of the future or, for that matter, of the present.

A slightly larger group are those who, like Rodolfo Machado and Jorge Silvetti, attempt to define classical "organizing principles valid beyond the sometimes superficial distinctions between classicism and modernity." In this they are not so different from modernists such as Mies van der Rohe, who also admired Schinkel and whose plans and buildings often were quite classical in their purity and proportion.

Here we are dealing not so much with style as with the basic stuff of architecture--open spaces, enclosures, relationships between parts--things that architects of all epochs must deal with. Machado and Silvetti's designs for the "Steps of Providence," Steven Peterson and Barbara Littenberg's competition entry for the design of Les Halles Quarter in Paris, and James Polshek and Peter Gluck's plan for a suburban development in Riverside, N.Y., are the projects falling most clearly in this category.

They also happen to be the largest, most civic-spirited of the items on view. And, along with Robert Stern's striking design for the DOM company headquarters in West Germany, they are the least classical in design details. This may be coincidence but, if so, it is a healthy coincidence.

Unless we are prepared to see new urban spaces along the lines of the classic-revival Federal Triangle, we must look to complex organizing principles, drawn from classicism, modernism and wherever else they are to be found, rather than to elements of a consistent revival style.

The dominant mode of this exhibition is anything but consistent in its application of classical principles or elements of classical style. This is what the ubiquitous British writer (and architect) Christopher Jencks has termed "free-style classicism," a "wide tradition not confined to the Greco-Roman alone" that is "based on the transformation of ideas across cultures and building types."

Many would object that "free-style classicism" is a contradiction in terms, but it is a handy, and accurate, moniker for the allusive, impure, ironic and ambiguous kind of architectural operations on view. There is much to admire, but also to question, in almost every project that fits this broad description.

The guest house conceived by Charles Moore (of Moore Grover Harper) for a conference center in Cold Harbor, N.Y., for instance, is skillful and ingenious in the way it replays a symmetrical Palladian villa both outside and in. But the angled circular entrance skylight seems a bit of needless braggadocio. The scale, colors and siting of a vacation house in Aspen by Michael Graves are really beautiful, but one wonders about the symbolism of his ambiguous architectural building blocks and questions the obviousness of the applique of local log-cabin construction on his sensuous surfaces.

Edward Levin's design for "An American Standard Home," with a recessed apsidal entranceway split by narrow columns, is quite pretty and seemingly straightforward. But am I missing the point? That entranceway apparently is a palimpsest of arcane architectural references. Helen Searing of Smith College, who organized the show, points out a sequence of historical references starting with Thomas Jefferson and moving backward in time through Claude-Nicolas Ledoux and Robert Adams to the Roman Baths of Agrippa.

Christopher and Timothy Morris obviously have picked the right problem when they attempt to unite "solar technologies and architectural aesthetics," but the cluttered classicism of their solution seems more an argument than a building.

And so on. It is easy to get impatient with much of this stuff, especially in this crowded little exhibition space--it can seem excessive, self-conscious, clever, abstruse, superficial, attention-getting and cute, sometimes all at once.

But there is a richness, complexity and seriousness to the ideas in the show, as well as a lot of good architecture, that cannot be ignored. Much of the exaggeration is polemical, and polemics are clearly needed to break down the resistant house of (by-now) hand-me-down modernism. In their different ways the architects in the show are responding to this challenge.

The exhibition, organized by the Smith College Museum of Art and supported by a grant from the National Endowment for the Arts, is circulating under the auspices of the National Building Museum. It will remain at the National Museum of American Art, 8th and G streets NW, through March 27.