There is much to wonder at, and about, in the exhibition of Leon Krier's architectural plans and drawings at the Museum of Modern Art, but Washington-area visitors to the show will doubtless spend most of their time in the hair-raising section he titles "The Completion of Washington, D.C., A Bicentennial Masterplan for the Federal City."

Krier, 39, is a European intellectual (born in Belgium and resident, since 1974, in England) who combines rebellious, passionate insightfulness about the ways we build our cities with marvelous skill as a draftsman and dreamy inventiveness as a designer. His wide-ranging critiques and steadfast insistence that there are better ideas and methods are refreshing despite the fact -- or perhaps because of it -- that Krier refuses to soil his hands in the dirty day-to-day details of getting things built. "Utterly estranged from the present day," Colin Rowe has observed, Krier "is still one of our greatest teachers."

"The eyes of the nation are turned towards Washington at all times," Krier writes. "Beyond being the symbolic heart of Democracy and seat of government I believe the Federal City is destined to become the touchstone and criterion for the rebirth of urban life and culture; of civilized social intercourse, of simple grandeur and elegant simplicity."

If such enthusiasm and optimism are, least to say, contagious, Krier's vision of how we might fulfil that promise takes some getting used to. No, it requires more effort than that. Beautiful yet appalling, magnificent but megalomaniacal, pragmat-ic though preposterously impractical, Krier's vision demands study and thought lest it be dismissed as the monumental pique of a vastly disgruntled genius (which, in part, it is).

In brief, breathtaking outline, what Krier proposes for the city's monumental core is this: obliterate Frederick Law Olmsted's Capitol grounds in order to fill them, on the east, with small residential-commercial neighborhoods and, on the west, with a big, paved open space (National Square revisited?); build in the Mall with similar residential blocks, preserving only a few of the museum buildings there and saving a narrow, water-filled strip at the center; connect and vastly expand the Lincoln Memorial reflecting pool and the Jefferson Memorial tidal basin, transforming them into a huge lake to which Krier would add, among other things, a pyramidal Civil War Memorial.

This is a mad scheme, so thoroughly destructive of the beauty that Washington already has -- Krier considers the city's core no more than "a grand skeleton with noble limbs but little flesh" -- as to be certifiably vicious. Neglecting, for the moment, the facts that it is art, not architecture, and that Krier's drawings of details of his grand plan are imaginative and enticingly beautiful, one must count to 10, slowly, before even asking the question: Is there method to this madness?

The answer -- Yes -- must indeed be qualified. Krier's strategy obviously is that of a brilliant architectural agent provocateur whose exaggerations are meant to instruct, to force a fundamental rethinking of the consequences of allowing things to go on as they are. Even so, it is hard to believe that his perversity is wholly under control -- to destroy much that is good (or even great) along with much that is bad in the name of a supposedly "better" order smacks awfully of the Modernist tabula rasa against which Krier is in open revolt.

Still, the more one looks, the more substance one finds. Take, for instance, downtown Washington, which is becoming more and more a massive single-use office district despite the District government's hapless call, in its master plan, for a "living downtown" (hapless because it has no teeth, no mechanism to ensure that people actually will live there). Krier's call for a city made up of contiguous "urban quarters," which "integrate all the functions of urban life," clearly is the more desirable blueprint.

Or take, for instance, the Federal Triangle, an area which, despite the sometimes overlooked architectural beauty of its classic revival buildings, has been an urban dead zone and a barrier between the city and the Mall for nearly half a century. Krier proposes partial preservation along with demolition and rebuilding to make another of his "urban quarters" there.

While this would be wasteful -- Krier for the most part is blissfully carefree about costs -- it is assuredly provocative in the best sense: Should not the Triangle be opened up in ways that he suggests (and that were, incidentally, suggested in more conservative form in a recent master plan for the area that is now gathering dust)? And could not, in the long run, the vast parking lots on the western edge of the Triangle be converted to living, as well as office, spaces?

Krier takes the medieval city as his enduring model, and on several general levels this absorption in architectural texture, horizontal density and active street life produces invigorating insights. For all of the damage his plan would do to Washington's monumental spaces and the city's openness, his emphasis on smaller blocks defined by plentiful streets is a powerful antidote to the bigger-and-bigger development parcels that have become business as usual in the city and its suburbs. (This is, in part, what the last-ditch debate about downtown and neighborhood historic preservation is all about; Krier simply insists that relative smallness, and genuinely mixed use, be the rules in new construction as well.)

But Krier's greater contribution as a theorist is his emphasis on the organic wholeness of the city and its component parts. He repeatedly insists that the social and architectural vitality of a city are interrelated, and that both are dependent on, as he says in his call for a "Global Ecological Reconstruction," cutting "environmental problems down to manageable sizes." Thus he uniformly prefers particular forms to generalized abstractions, takes his cues from traditional rather than 20th-century architecture, and insists that the forms (the buildings, streets and public spaces) be intimately related to each other in distance, scale, materials and, loosely, style.

Small wonder that Krier was attracted to Washington: This mid-rise city, based on a superb Baroque plan and still dominated by just a few astonishing, symbolically apt, vertical monuments, is one of the few left on the industrialized Earth that still fits his medieval morphology. If, taken literally, much of Krier's plan for the city's monumental core would comprise a blueprint for disaster, taken metaphorically it does its work, provoking a healthy shock and then some.

Krier's art -- his magic -- is to be able to visualize his theories with an inventiveness and skill that would be the envy of any great architect. But Krier doesn't build buildings. He dreams them. By dint of his enormous skill as a draftsman he is able to raise the act of architectural dreaming to the level of art, and in so doing fills our minds with memorable visions.

As Jaquelin Robertson has written, when confronted by a sequence of Krier's drawings, which typically progress from a plan through many detailed designs, "One thinks of stone and timber and tile and finely wrought metals; of solidity. Krier evokes our collective cultural memory of low, dense, small, simple buildings, defined streets, great squares and high-roofed public halls; of tree-lined escarpments and distant views; a setting at once timeless and archaic and yet startlingly fresh and new." Krier evokes, in short, possibilities for architecture that, enmeshed in the present, we often forget.

Krier's show, in company with a fine presentation of Ricardo Bofill's recent works in France (challenging, because actually built, in a thoroughly different way), continues through Sept. 3. Someone should bring it to Washington.