At 1911 Pennsylvania Ave. NW, architect Peter Vercelli has added a striking and justifiably controversial new entry to the evolving lexicon of ways Washington designers have devised to combine new with old architecture. Vercelli's new building fairly screams its antagonism to postmodern contextualism -- it is all tensed 20th-century muscle, an isometric exercise of cantilevers, sun screens and concrete beams enveloping two fine late 18th-century houses, sole remnants of the so-called Seven Buildings. This is a project Washington preservationists love to hate, but it undeniably has the courage of its convictions. The composition presents an unforgettable image; the whole is a harsh set piece of contrasting styles, materials, epochs and scales. The concept, Vercelli says, was to combine the "two time locks" in a way that "borders on a kind of reliquary, where you see St. Theresa's finger bone enshrined," and that is the interesting, tension-filled effect. One does perceive these old flat-front brick buildings, with their pitched roofs, exquisite dormers, arched doorways and delicately mullioned windows, as antiques, treasures, relics. And one does comprehend in a flash that their time has gone by. Those who condemn this project fast and outright should pause to consider its actual context. Ideally, of course, we'd still have with us the entire 18th-century row, where vice presidents, senators, congressmen, diplomats and even, for two years, a president and his wife boarded when the city itself was new. It is a minor oddity of D.C. history that the Seven Buildings actually were six in number, while the long-vanished Six Buildings farther to the west along Pennsylvania Avenue actually were seven. In any case, one of the six Seven Buildings was demolished in 1898 and three others, including the crucial corner piece, were taken out three decades ago. So what this architect had to work with was in itself an odd and unsettling situation. He was charged with restoring two midblock historic structures, both significantly disfigured (one housed Marrocco's Sorrento room, a local landmark of sorts), and building the relatively narrow, shallow lot to its full economic potential under current zoning regulations. As bookends he had two undistinguished products of the '50s and '70s, respectively -- to the east the curtain-wall office building that darkly occupies the northwest corner of 19th and Pennsylvania, and to the west a bland, gray ribbon-window structure stretching to the corner at 20th Street. In this context, the conventional wisdom of stepping back the taller structure would have made very little urbanistic sense. Vercelli's staggering of the upper floors is in fact a reversal of the stepped-back massing employed by the architects of some of our best recent blendings of new and old -- one thinks of Hartman-Cox's building at 1001 Pennsylvania Ave. NW, with its two-tiered arrangement of 20-foot setbacks, or of David Schwarz's supple modulations behind a Victorian row at 1919 N St. NW. Here, the new building steps forward toward the top, making a prepossessing form reminiscent of Marcel Breuer's Whitney Museum in New York and, more pertinently, carving out a space for the restored houses. Similarly, the strategy of historical replication, of styling the new piece in the manner of the old, would have been out of place. Vercelli thus breaks two very good rules, but for good reason. His idea of framing the historical buildings like a stereoscopic picture, of making a dramatic three-dimensional postcard, seems at once brilliant and inevitable -- the right solution in the right place. This is not to say we're talking harmony here, nor elegance, nor civility. The contrast between old and new is bold, to be sure, but it's stagey, too, as if contrast were defined in part as conflict. The reliquary sets off the relics, and then contests them: From a frontal view, the old houses seem impaled upon horizontal concrete beams and ribbon windows. The staccato rhythms of the new facade jarringly insist upon their own self-importance. Even the colors are wrong; where grays are called for there are beiges and tans and bronze-tinted windows. Nor is the interior lobby-atrium anything to write home about; by necessity squinched between old and new, it is an uncomfortable space, rawly detailed. The choice may not have been available, but Vercelli's idea would perhaps have been better served had he abjured this throwback style -- which recalls the "Brutalism" of 1960s modern architecture -- and opted instead for low-key, high-tech finishes. He certainly would have done better all around had he designed the new piece in a lower key; he made what's often called a "foreground" building in a place that calls for background. But it is what it is: The building can be thought of as an imperfect but passionate metaphor about the continuous processes of change and growth in cities. With unquiet authority it presents two different scales of cityscape and stills two moments in time, and it is this sharp, pictorial, almost archeological quality that appeals. The project is remindful of Shalom Baranes' additions to the Army-Navy Club on Farragut Square, though the two are far apart stylistically. Each is flawed, but each in its way dramatically etches the dividing line between time past and time present. Such linguistic impressions aside, the Vercelli project does bring back two time-honored treasures, and does so with an admirable degree of fidelity to the originals. The absence of English basements is unfortunate; without them the buildings with their raised front porches look as if they've been prepared to fend off a flood. Also, these are Georgian-Federal halves, not wholes -- the rebuilt interiors extend only to the ridge line of the roofs. That's more or less par for the course on downtown lots where present-day zoning allows densities far greater than imagined 200 years ago. It is not a model one would recommend in the as-yet-undeveloped downtown historic district, but in this particular place, it clearly was the best deal available. I've heard it said around town that here the best deal was not enough, that the new setting so transforms the old that the old wasn't worth saving. Baloney. Whatever else one thinks of this vivid image, after passing it one won't quickly forget that behind windows just like these President and Dolley Madison, among many other movers and shakers of the time, once looked out upon a graveled grand boulevard.