In 5,000 years of urban design -- it dates back to the cities of Ur and Babylon -- there is nothing quite like Robert Venturi's Western Plaza. a

It is supposed to be a sort of side dish for the visual and urbanistic feast that is to be the new Pennsylvania Avenue and is located in front of the National Theater and opposite the District Building. It is also no plaza at all, but a literary traffic island, a pedastal without a monument, a vast, woefully overdesigned observation platform.

In textbook definition, a plaza (saying "square" in Spanish is supposed to make it more sophisticated) is a clearly contained urban open space. The word "space," however, is so horribly abused in our jargon-infested world of modern art and architecture, that it may be more comprehensible to call a "square" a city "living room" whose floor is paved, whose walls are replaced by enclosing buildings, whose ceiling is the sky and those furnishings are fountains and other useful and/or decorative street furniture.

A square can be vulgar, like Times Square in New York. It can be nondescript, like Thomas Circle. Or it can be very elegant like the Place des Bosges in Paris. It can serve as a gathering place, like the New England village greens; an outdoor market, like most medieval squares; to provide a forecourt for an important building, like the greatest square of them all. Michelangelo's Campidoglio in Rome, which sets off the Palazzo del Senatore; or as a monumental place, like the Place de la Concorde in Paris. s

People remember cities more often because of their squares and avenues than because of their buildings. The Piazza di San Marco in Venice is as widely known as Leonardo da Vinci's Last Supper.

But to be memorable, a square must be designed to the human scale -- another trite bit of art babble, but a precisely definable one. In the case of squares it means that the dimensions, the sense of enclosure, must be easily grasped. Urban designers, such as Paul Spreiregen, have measured exactly what the human eye can take in all at once to make the mind comfortable and the heart happy.

The human field of view, for instance, measures about 30 degrees up, 45 degrees down and 65 degrees to each side. The maximum distance at which we can tell whether a person is selling newspapers or hailing a taxi is 450 feet. A square that exceeds such dimensions ceases to be a pleasant experience. It is not nice to feel dwarfed.

Western Plaza disregards all of this. It is not defined, being bounded by moving cars, not buildings. It is too big -- 600 feet long. It is not a harmonious unit, according, consisting of three loosely glued-together parts: 1) The equestrian statue of General Casimir Pulaski on a skimpy patch of grass, 2) a huge, marble floor poster and 3) a big fountain.

And it is not really a city square because the basis of a city square is, of course, its paved floor and you cannot see that as you pass on foot or by car. The thing is raised three feet above street level. That is just high enough the lift it right out of the city. What the citizen sees (unless he is on an upper floor of an adjacent building or in a helicopter) is a low wall with steps, railings, shrubs and big funereal urns.

All this was not readily apparent on the design drawings.

What you find when you climb the three steps to the top of the platform, is a pavement of white marble and dark and light gray granite depiciting the center core of the L'Enfant Plan of Washington. It is, however, almost impossible to read, because the scale is far too big and the various elements too far apart to relate and form a coherent whole. Being right on top, the different colors of stone form only an abstract pattern.

The Plan's lettering is engraved into the pavement pattern and so, scattered around at random, are some 30 or 40 quotations about Washington in three different styles of lettering. That's a lot of literature and a lot of type specimens.

Passing the platform, you see all the people up there looking down as though they had dropped their contact lenses.

The weird platform came about when the Pennsylvania Avenue Development Corp. straightened out the traffic pattern on that end of the avenue. It makes sense clearly to separate E Street from Pennsylvania. But what to do with the no-car's land is between?

The answer was two squares. One between 15th and 14th streets is to be a park with lots of trees, benches and a Pershing memorial. It has been designed by landscape architect Paul Friedberg and will be completed next year.

The Western Square (which is actually east), between 14th and 13th streets, was to be hard and urban. Originally, architect Robert Venturi was to work with sculptor Richard Serra, but Serra resigned the commission.

Venturi first came up with two pylons -- to frame the view of the Capitol and give the avenue a focal point, a vertical marker somewhat like the obelisks on Baroque avenues. I thought it a brilliant idea, just what was needed.

But Venturi so burdened his idea with stars and flags and complexities, that it collapsed. That left his pedestal without a monument, a giant gravestone for another of this city's magnificent intentions.

With hindsight, it seems that once his pylons were knocked down, the best hope for this traffic island would have been either to make it an elaboration of the Pulaski monument or a forecourt for the National Theater. e(The District Building is too distant to establish a relationship.)

Perhaps Venturi failed with this plaza because he doesn't like plazas or "piazzas" (the Italianized word planners use for squares when they want to make them sound folksy like pizza) as he calls them in his book, "Complexity and Contradiction in Architecture." Published in 1966, it is a gentle attack on the International Style school of architecture and made Venturi famous.

The open piazza, Venturi wrote, "is seldom appropriate for an American city today except as a convenience for pedestrian shortcuts. The piazza, in fact, in 'un-American.' Americans feel uncomfortable in a square."

I am afraid we will in this one.

Andrew Barnes, the director of the PADC, says that the Western Plaza design is not necessarily final. "The city is forever changing," he muses. "We might be changing the plaza, too."

The one thing Barnes should not change is the view from Venturi's platform. It is magnificent.