Even though the developers who decided to build the Grand Hyatt Hotel in the old downtown got three things right -- location, location, location -- one is hard put to get enthusiastic about the architectural imprint the new building makes. It's polite enough, for so big a building, but its historicism is halfhearted. It could be called the Semi-Grand.

This is not to say that the architects, RTKL Associates, did not do a bang-up job for the Quadrangle Development Corp. in putting together the myriad pieces necessary for a successful, convention-oriented, midtown hotel in the 1980s. The vast atrium-lobby -- based, of course, upon the model reinvented by architect-developer John Portman in Atlanta two decades ago -- is a marvel of animation, a vivid stage set for busy comings and goings. But the whole comprises a strange, unsettling mix.

Outside we get a dead-serious reminder of yesteryear's grandness -- rest your weary bones in luxury here, behind these bricks and stones, the building tries to say. Inside, the grand of old is speeded up. A sophisticated confection of no definite period or style, this space is a vaguely Mediterranean Arcadia designed obsessively to celebrate 20th-century scale and movement.

If the inside is odd, almost surreal, it is the best part of the new hotel. There's scarcely a moment's peace here -- even the blue-tiled "lagoon," a multifountained centerpiece of the atrium, is so choppy one fears for the well-being of the Japanese carp whose customary settings are Zen-still ponds. But there is plenitude -- movement, always, and a profuse flow of sensations.

The floor plan was devised with a touch of genius not only to control pedestrian circulation but to encourage it and to highlight it. The hotel is situated on H Street between 10th and 11th streets NW, immediately to the south of the Convention Center. There are flashy brass entrance doors on each street; those on H Street are perhaps best for a first visit. One passes through them onto a circular platform from which to appreciate the space by looking up, at the skylight towering 13 stories above, or down, at the lagoon with its piano island and restless carp.

The space in itself is not unusual. But the architects have made it so by carving away at the inside of the box. There are the equivalent of five floors underground; the ground floor, consequently, is a series of platforms and bridges, from which one descends on diagonals by stairwells or escalators to the lagoon floor, and from there to banquet and meeting room floors even further underground. It's a Piranesian sort of space, but relentlessly upbeat -- there are many different ways to get to the same place in this hotel, and lots of good vantage points from which to observe the to and fro.

The economic value of such spaces, to the hotelier as to the office builder, is to maximize the number of rooms with views. On the upper stories of the Grand Hyatt this empty rectangle is framed on three sides by double-loaded corridors, so that each of the 907 rooms looks either outward, to the city, or inward, to the courtyard. As many a Portmanesque atrium has demonstrated, this arrangement often produces bland, monotonous walls.

RTKL Associates (Bernard Wulff, principal in charge) pretty well solved this problem, and also provided a sun screen for many south-facing rooms, by attaching a sort of Mediterranean sequence of warm-toned pilasters and segmented arches to the north interior wall. This motif, continued in descending steps on the east and west walls of the atrium, sets the stage for the campanile towers on the south wall. These towers, housing the requisite cheap-thrill elevator cabs, are strong, strange, where-am-I forms -- a touch of de Chirico in a people place.

There are lots of ho-hum hotel details here and quite a few good ones -- one doesn't know whether to credit RTKL or Hirsh-Bedner, a California interior design firm, for either. Beautiful, simply detailed white maple walls on the banquet room floors add an unusual taste of tranquility; the railings on the interior balconies, with those acrophobic views, are simple and apt; and though the decor, as usual, often makes good art look like hackwork, on the long escalator ride down to Sublevel 3 there are spectacular niches for two superior cubistic pieces by California artist Guy Dill. This is perhaps the only place in the ensemble where present and past, modern and postmodern, come together in a scintillating way.

About the exterior there is not a whole lot to say. There's a certain staid rhythm to the minimally modulated fac ades -- the metal framed and spandreled window bays work in quiet concert with shallow, metal-railed "balconies" -- and there's a certain power in the rusticated stonelike base. The ground-level arcade is quite graceful; even the required fire doors, dead spaces on the street, have been tastefully framed; and there are corner entrances to a bar and to a deli-restaurant that will enliven H Street, which, with the Convention Center opposite, is deadly dull.

But it's a cold, passionless design. The mansard roofs, one punctuated by broad, pedimented dormers, the other simply masking service equipment and the atrium canopy, are flat cliche's. True, this building is better than a brutal box; we see the architects conscientiously hitting a lot of the right urban design keys without creating a wholly pleasant, let alone a memorable, melody.

But if it's a schizoid design -- outside attempting to say "Washington," inside speaking a garbled, if sometimes powerful, language of a timeless somewhere -- it clearly is an efficient one. And it's in just the right place, sitting across from the Convention Center, almost atop Metro Center and within easy walking distance of Chinatown, major department stores, museums, theaters and Pennsylvania Avenue.