Among recent works by Arthur Cotton Moore Associates, an architectural firm that has added many a distinguished piece to the Washington puzzle in the 20 years of its existence, are two sharply contrasting buildings -- the one a whopping, though valiant, failure and the other an ingenious, though flawed, success.

The clinker is on a prominent downtown corner. Despite the architects' well-nigh frantic attempts to give texture to the basic box, the office building seems intrusive, almost bombastic.

The triumph is a set of mixed-use structures at the eastern edge of Georgetown, which, despite the unconvincing touch of all-glass mansard roofs atop the principal new facade, does much to establish a new sense of place in a highly visible location.

This apples-and-oranges comparison is perhaps unfair -- the projects are very different in size, function and location -- but it is instructive. It underlines the difficulty of designing buildings in downtown Washington, where height limitations, zoning regulations and leasing economics push in the direction of the ribbon window box, but again proves that the constraints of a historic district such as Georgetown can stimulate imaginative, responsible architecture.

Moore and his colleague Kenneth Simmons certainly deserve As for effort in the design of 1400 I St. NW (called the United Press International Building after its principal occupant). In addition to the customary requirements (height, density and so on), they faced a formidable structural obstacle in that the thin membrane of a Metro tunnel under the site would not support a normal office building.

Thus necessity accounts for the eroded quality of the corner building, in which three tall, concrete piers support the upper floors while the street-facing portions of the lower floors, whittled into gentle curves, are suspended from the top. Moore's intention was "to give dramatic expression to the structure" and "to create a lively urban space" in the open area under those hanging offices.

Because the client (The Lenkin Co.), Moore says, rejected any window treatment other than the standard strip, the architects pulled out all stops in a tour de force try to negate the humdrum appearance of the typical banded building. They changed materials, from brick spandrels on the lower floors to concrete at the top. They changed glass and mullion colors. They altered window proportions. They indented bands here and there. They exposed structural columns on certain levels.

And on the exposed ground level they strove mightily -- one can almost hear huffing and puffing in the drafting room -- to enliven the surroundings with such things as an Art Nouveau gate framing the office entrance, a trompe l'oeil sky painted on the ceiling and Art Nouveau railings (ingeniously formed from off-the-shelf steel pipe) for the stairwell to a burrowed bar. (Moore complains that the design is "incomplete." He planned a kiosk as a centerpiece for the ground floor open space and a striped pattern for all of the brick spandrels.)

Unfortunately, the effect of all this mental enterprise is somewhat chaotic and decisively odd. The cutout corner does have potential as a satisfying urban shortcut and the building's very oddity may make it likable in the long run. Still, the concrete stilts are ungainly. The Art Nouveau elements, especially with their obnoxious yellow color (which, Moore emphasizes, he did not choose), look pasted on, like knickknacks from another world. The ground-floor storefronts are standard K Street issue. The ribbon windows, despite the variations, are faceless in the usual way. The building as a whole lacks unity and grace, and one can't help thinking, once again, that even in the hands of well-meaning architects this is a formula whose time has long since gone.

(The same conclusion applies, only more so, to the adjacent midblock building at 1444 I St. NW, designed by the Moore firm for Western Development, where the reverse curves and bays on the fac,ade serve mainly to call attention to its unlovely textures. Rococo exuberance and speculative economics are perhaps not an ideal match.)

Happier conditions applied to the Georgetown project, which involved the rehabilitation for office use of an 1880s schoolhouse (the Corcoran School) and new construction for commercial and residential purposes. This complex program and the challenge of building on a gateway site along M Street between 28th Street and Rock Creek Park allowed Moore (with the principal assistance of Ik Pyo Hong) to exercise his proven skills as an urban designer as well as his sense of humor.

The many pieces of this project -- the schoolhouse (complete and occupied), five town house units (still under construction) at the rear of the site and a new building (almost finished) to accommodate nine split-level condominium apartments, offices and shops -- hold together quite splendidly.

Much of this is due to the site plan, which, by providing separate entrances to the schoolhouse office off 28th Street, to the residential units via a fenced-in mews and to the office building and proposed shops along M Street, is a marvel of economy. So, too, is the floor plan for the office-residential structure, which neatly squeezes in both uses.

The picturesque style of the new M Street building, with its corner turret reminiscent of many nearby Victorian-era homes, fits this section of Georgetown perfectly. The profile is apt, too, as the building steps down to an existing two-story building (not part of the project) on the northeast corner of 28th and M streets. The windows are appropriately varied in shape and finely made.

Furthermore, appealing details abound, from the superb brickwork of the new structure to the tiled cascading fountain in the mews to decorative touches around and about, such as the little look-Ma-no-marble colonnade with pediment gracing the top of the garage entrance. It is welded together from store-bought steel parts and it ought to look silly, but doesn't.

If there is a single major fault to find here it is with the roofs of the new structure -- modernistic mansards sheathed from top to bottom with sloping glass panes. Doubtless these provide excellent light and views, but their sleek transparency contradicts the richly textured masonry surfaces of the building, and thereby give it an unfortunately ad hoc appearance. All things considered, though, this is a flaw we can learn to live with.