One can already see the bare-bones outline of the clock tower of the Presidential Plaza, an office building under construction at 19th and I streets NW. It is a most welcome sight.

This particular intersection does not rank terribly high on the list of Washington corners, which, thanks to the city's baroque street plan, includes some of the oddest and most beautiful in the world. But the place has its appeal -- one gets a good view of it both from Pennylvania Avenue and K Street -- and the middle-sized clock tower suits it perfectly.

Furthermore, with its sleek sculptural form and its banding of clear glass and pinkish granite, this tower is an elegant thing that, like much else in the design by the firm of Keyes Condon & Florance, helps to set a standard of civility for unbuilt corner sites elsewhere in the city.

In general, sleek ribbon-window office buildings are a terrible idea in downtown D.C. Wide or narrow, dark or light, row upon row of uninflected window bands make many recent Washington buildings look like so many slices of woebegone layer cake. They threaten to turn the streets -- have you seen 14th Street lately? -- into a bad dream of the most cliche'd, anti-urban sort: everywhere a faceless flattop box. To say they vastly overemphasize the city's horizontal skyline is being polite.

So, it is no small achievement to create a ribbon-window building that contributes in a positive way to the character of the city. It has been done before, most recently at International Square, which, with its handsome concrete detailing, is one of the city's best such structures (Vlastimil Koubek, architect).

International Square sits directly across 19th Street from the Presidential Plaza, and to the southeast the new building looks upon an unusually polite, if mildly boring, modern building occupied by the World Bank (Weihe Black Jeffries Strassman and Dove, architects). On the southwest corner sits an unpraiseworthy, if innocuous, office building designed by the same firm in a similar, mid-'70s Modernist vocabulary.

Hence the designers of the Presidential Plaza were simply playing by the rules of the contextual game by wrapping their box in clear glass stripes. Fortunately, they outdid their colleagues. "We were seeking a sort of Viennese, 1920s, Moderne feeling in the overall design, with a touch of New York elegance where the building meets the street," says partner Colden Florance, who with project architect David King was primarily responsible for the design.

This is very much like saying, and then proving, that a mid-rise Modernist office building doesn't have to be offensive or dull, and it is interesting to note that, at the same time they were paying close attention to the nearby structures, the architects were looking back, in theory, to a time when Modernism and ornamentation were not mutually exclusive terms.

(Ironically, it was a Viennese architect, Adolf Loos, who decreed ornament to be a crime, although in practice most Viennese architects didn't pay too much attention to the purist theory. Had they done so Vienna would not be Vienna. Loos' unhappy argument had a much greater effect in American cities.)

A consequence of this thoughtful approach is that the abstract ornamental scheme of the Presidential Plaza promises to be one of its principal attractions -- from the beautifully integrated stripe patterns of the facade to details such as the clock face (a svelte adaptation of a design by Viennese architect Otto Wagner) and the elegant Moderne-type lighting sconces on the walls between ground-floor store windows.

There is another thoughtful treat. Not only is the entrance to the stylishly appointed office lobby located in just the right place -- underneath a canopy formed by the clock tower -- but the inset display windows, each with its striped awning, actually look like shop windows, in contrast to the blatantly boring norm in this neighborhood. And passers-by will be able to get close enough to touch those lovely polished granite panels -- a small but appreciable bonus when one considers the number of modern buildings in the area one wouldn't want to touch even with a 10-foot pole carried for such emergencies.

The Keyes Condon Florance firm is currently designing another office building in the area (like the clock tower, for the Oliver T. Carr Co.) that, though quite different in materials and style, promises to complement its corner in similar ways. To be located at 18th and I streets, this one, too, will have a tower (perhaps with bells instead of a clock, Florance says), a patterned surface (a basket weave of bricks and precast concrete), and handsome details (urns and ball lights at the roof line, pretty tripartite windows in the middle).

It is too early to analyze this design in any detail, but not too soon to say that it, too, represents a sizable improvement in architectural quality for the "new" downtown west of 17th Street. The low-key elegance of the Keyes Condon Florance approach stands in sharp contrast to the robust muscularity of the turreted building the Washington office of Skidmore, Owings and Merrill designed for the corner of 20th and K streets, but this is the kind of argument between architects that one likes to see.

Each of these buildings, with their handsome masonry facades, will add a touch of class to its corner; each will insert a welcome note of variety into the city's flat, low skyline; each will enliven the streets it faces. Best of all, each will establish a sense of place in locations that very easily could have become the sort of non-places we've become too familiar with in the last 25 years. It will be a pleasure to tell time from the city's newest clock tower.