The fast first reaction to the architectural expansion announced yesterday by the John F. Kennedy Center for the Performing Arts has to be this: It's about time.

From opening day 31 years ago right up to the present, the big box on the Potomac has remained a huge urban faux pas -- an outpost of culture separated from the city by a deep moat filled with speeding cars. The plan unveiled yesterday, conceived by architect Rafael Vin~oly, does a lot to correct the mistakes.

The major move is to cover over that humongous moat -- otherwise fondly known as the "spaghetti bowl" because of the confusing tangle of highways running through it. This welcome cover job has been in the offing for some time -- the Kennedy Center and the Department of Transportation last year announced their intent to collaborate on the task.

But the idea of building over that mess of macadam is one thing. Doing it with sparkle and grace is another. Vin~oly's plan (see related article, Page A1) manages quite a bit of both.

He proposes, as a daring start, to cover the roads not merely immediately to the east of the arts complex, but extending eastward to the 23rd Street overpass over E Street. Reclaiming all of this territory -- a distance equivalent in length to nearly five football fields -- promises to give the Kennedy Center two things it's always lacked: a striking, direct link to the city for both automobiles and pedestrians, and a distinguished, urbane setting.

Though this would be Vin~oly's first major undertaking in Washington (he was one of six finalists in the World War II memorial competition), the Uruguay-born, Argentina-educated, New York-based architect appears to feel right at home here. His proposal elegantly embraces the spirit of Maj. L'Enfant's plan for a city of broad boulevards and long, formal vistas.

Picture this: You are standing on 23rd Street during a May evening, looking west, toward the Kennedy Center. Edward Durrell Stone's banal concoction of gold comic-book columns with white marble walls is dramatically lit and, actually, looks pretty good because it lies at the end of an alluring axis. Trees frame the view, and there is a long pool of water that gradually widens in the distance, culminating in a large circular fountain.

It is not a distance you would want to walk on a cold day, but it is springtime, after all, and the fountain beckons. So you venture forth under the trees, noting as you proceed how the sidewalk and roadway begin to curve gently outward. Glass-and-steel buildings frame the path both north and south. They, too, fan outward, so that when you reach the fountain you get a full view of the paved, oval plaza -- a spacious platform the large building has long needed.

This is really a very dandy, very Washington kind of plan. The connection to the city is perhaps more symbolic than real -- not a whole lot of folks are going to start from downtown and walk that long walk. But symbolism is important, and Vin~oly here handles it with sweet sophistication by expertly manipulating perspectival views.

Nor is this grand eastern approach the only improved link between the Kennedy Center and the city. By continuing his curving platform all the way around the building, Vin~oly also makes possible several other important pedestrian connections -- notably, a bridgeway that would provide access to the Lincoln Memorial grounds, and a long-proposed link from the west esplanade to the parkland alongside the Potomac. (Vin~oly envisions this connection in the form of two long ramps, to comply with federal disability access standards.)

Automobile access to the Kennedy Center and its parking garages would not be tinkered with too much. But arriving there by private car or taxi (or limo) via that new eastern road certainly would be a splendid new way to begin a night at the opera.

Though Stone's building was plenty big enough for three large performance halls, it did not provide much administrative or rehearsal space. Nor did it have much expansion room to accommodate the center's growing educational programs.

Indeed, these needs were the driving forces behind the Kennedy Center's plans to expand. It asked for a plaza and two buildings, one on the north for offices and three large rehearsal stages, and one on the south for educational facilities and a performing arts museum.

At this point, there is not a whole lot one can say about the architecture in Vin~oly's conceptual proposal, except that he appears to be off to a good start. For one thing, he beautifully deploys the two buildings to shape that eastward approach and frame the new plaza -- architecture in its placemaking role.

For another thing, Vin~oly seems to have intuited a shipshape aesthetic vocabulary that would complement Stone's and yet not stoop to mimicry. His design calls for long, sleek, curving buildings with lots of glass and dramatic canopies supported by tall steel columns. The idea is to contrast lightness, lowness and transparency with the center's stark opacity -- a worthy notion.

For sure, not everything about this plan is sweetness and roses. The plaza may be too big and too undifferentiated. Those ramps leading to the riverfront park, obscured by the oval overhang, seem way too dark. The overhang itself, projecting out over the river, may be a bit too much. The buildings could turn out to be too stark. And so on. This project will take a long time to build and will need many a change along the way. It'll need careful watching, however, to make sure the changes are for the better and not, as so often happens, for the worse.

Vin~oly -- whose famous public buildings include the striking Kimmel Center for the Performing Arts in Philadelphia and the immense, multi-layered Tokyo International Forum in Japan -- won out over a select list of 28 architects. He appears to have been a splendid choice.

The architect's concept for the Kennedy Center expansion would sweep visitors past new rehearsal and education buildings.Rafael Vin~oly was selected from among nearly 30 architects to remedy the Kennedy Center's space and isolation problems.The view east from the Kennedy Center along Rafael Vin~oly's proposed extension of E Street, part of a plaza that would cover the current tangle of roadways separating the center from the rest of the District.