Architect Arthur Cotton Moore's bright little addition to the northwest corner of L Street and Connecticut Avenue NW is a building with many missions. It's a sign, an entryway, a means of getting from here to there, and also an alluring oddity that enlivens one of the city's busiest intersections.

The practical reason for its existence was the need to entice customers to move up and into Rizik's, a fine old emporium of women's clothes that recently relocated to the second floor of the 1960s office building on the corner. On a basic level the new piece is a simple conveyance, a framework of concrete, steel, granite and glass for a stairwell, elevator and bridge. But this is a very fancy conveyance, and appropriately so.

With its swirls of steel, metal pennants, spiral staircase, brassy elevator carriage, sheets of plate glass elegantly curved and mannequins brightly dressed and lit, the new building celebrates the inherent theatricality of fashion, of shopping, of city streets. It is what the late urban theorist Kevin Lynch would have called a "point reference," a minor landmark that creates a vivid new identity and sense of place.

The story of how it came to be has several interesting twists. One concerns the Rizik family, which founded the store 82 years ago on F Street in the old downtown center, purchased a building at Connecticut and L and moved into it in 1933 and then, in a real estate deal, had it torn down in 1965 in favor of a speculative office building. At that time the shop was relocated two blocks northward onto two floors of an innocuous modern building at Connecticut and N.

So in a sense, the recent move represents a return home for both family and store. Taking advantage of the fact that it owns the building at Connecticut and L, the family was in an ideal position to move, says Philip Rizik, when the Merrill Lynch office vacated the second floor. "We were bursting at the seams," he explains, "and the new location offered us 50 percent more space, from 8,000 to 13,000 square feet. And it was all on one floor, so we could integrate and expand our operations."

The marketing advantages of the return were obvious too. This is indeed a special corner, close by a major downtown park, the Mayflower Hotel and both Connecticut Connection and Washington Square, buildings that directly link commerce with the underground Metrorail system. But there remained a significant disadvantage -- operating a store one floor above the sidewalk has been a curse to many a Washington retailer.

In this too, the family's familiarity with the building proved a help. Ironically -- for such clearly was not the intent -- the original configuration of the building, designed by Chloethiel Woodard Smith, provided the space needed to solve the access problem. "The architect wanted to do something special," Rizik recalls, "so she set the building back a bit from the property line" in order to shape a hard-surfaced little plaza. A praiseworthy gesture, decently if not compellingly designed, the plaza suffered poor maintenance and general abuse over the years. It won't be sorely missed.

There's a certain irony as well in Moore's enlistment in this project -- as a young architect not long out of Princeton, he was working in Smith's office when the Riziks' building was being designed. (It was the second of three buildings at this intersection that Smith designed -- Connecticut Connection being the sole exception. Among architects, the place is often referred to as "Chloethiel's corner.") One does not glibly endorse the taking of a public space in favor of a private structure, of course, nor does one lightly forgive an architect for intentionally upstaging the work of his former boss. But if Moore and his clients are guilty on both counts, they can wear their guilt with ease, for the benefits of the new arrangement far outweigh any loss.

For one thing, Moore's striking new building and its carefully designed surround don't take away all that much in the way of usable public space. The architect here employs his patented S-curves to benign effect. The curved display windows, secured by bands of steel, carve out a sidewalk niche for a cylindrical planter built, as was Smith's fountain, to ideal sitting height. Passersby will be tempted to perch there close by the mannequins as if at a fashion parade or, in the architect's analogy, as if happening upon a cocktail party.

Furthermore, though the design is a bit heavy-handed at its scrolled top of polished granite, it undeniably establishes a memorable new image of commercial vitality on this corner. This is fully and dramatically in accord with the genius of this place as it has developed over time. The building says "busyness" and "business" as clearly, and more effectively, than would a sign literally spelling out the words. It is in itself a sign, not only for the store it serves but also for the more complex concept of urban dynamism.

But perhaps we get too ponderous. The building is about shopping, neither an unserious subject nor a mighty one. Moore transforms the simple activity of entering a store into a ceremonial event: One ascends the stairwell or the elevator like a prince or a pope, crosses the bridge and enters ... a store totally designed by Moore! Scrolls and S-curves everywhere; everywhere warm materials and tongue-in-cheek elegance. The layout, with countless nooks and crannies, fits Rizik's time-honored MO of circumspect saleswomanship to a T. (Oops. Let's say it fits to an S.)

All things considered, Moore's upstaging is as gentle as can be. Sure, he uses Smith's quilted facade of polished granite slabs and dark rectangular windows as a backdrop for his emphatic addition. But clearly he took care to ease the transition by selecting complementary, warm-toned materials and colors and by modulating differences in scale. Attached to its modern parent by the umbilical cord of that second-story bridge, Moore's postmodern building seems, strangely, like a natural-born child.

There are places in this town (and others) where such a design strategy is uncalled for -- one thinks, for instance, of the entryway Moore created for a modest office building at 1800 I St. NW, so cheap and jeering. And one continues to wonder about the effects of "industrial baroque" -- Moore's name for his effervescent late style -- when applied at super scale, such as the Moore-designed Portals project under construction in Southwest Washington. But the architect seems comfortable, even masterly, working in the scale and commercial milieu of Connecticut and L. If there is an ideal spot for his idiosyncratic brand of playfully opinionated contrast, this is it.