It will take a year or more before all the finishing touches are applied to Market Square, the big new complex on Pennsylvania Avenue between Seventh and Ninth streets NW. But, with just a bit of imagination, it is already possible to see that this is as thrilling a union of private buildings and public spaces as we will see built in Washington for many years.

Geometrically, the new place is misnamed. This is a paved circle defined by two big new buildings. Nor does the notion of "market" accord all that well with the new circumstances -- the dignified open space is a far cry from the lively long-gone marketplace of the late-19th and early-20th centuries that provided the excuse for the name. By its very size and form, the new place tells us that Pennsylvania Avenue as reconstituted is much more a ceremonial boulevard, and less a Main Street, than it used to be even a decade ago.

This is regrettable, but only up to a point -- the new avenue, though still lacking the vitality of commerce, offers its own particular excitements. Sen. Daniel Patrick Moynihan (D-N.Y.) who advanced the cause of the avenue's redevelopment under both Presidents Kennedy and Nixon, was on hand to anoint the new image at Market Square's grand opening last night.

"The ambition of every American architect," he said wittily, "is to design a Parisian boulevard and an Italian hill town. And I must say that, thanks to the efforts of {a long list}, what you see from up there on the balconies is just that." Moynihan and his wife, Elizabeth, did more than vote with words -- they have bought one of the apartments.

Market Square, in any case, is chief among the avenue's new appointments. People will be attracted to this nonmarket unsquare simply because of the fact that what it does, it does extremely well. Combining architecture with urban design, commercial with symbolic uses, elegant propriety with ceremonial pop art, it's a very, very Washington spot.

The core of the space is the U.S. Navy Memorial, which has been more or less done for several years but has been hard to appreciate through the web of construction fences, cranes and dust. Now, however, with most of the obstructions removed, we can see how it fits its environment like a key in a lock. Sculptor Stanley Bleifeld's bronze figure of "The Lone Sailor," standing windblown on that map of the world engraved in the sloped, circular pavement, no longer looks so all alone.

With tremendous mid-level colonnades in the Roman Doric order adorning their curved facades, the new buildings, designed by the local firm of Hartman-Cox, are stentorian landmarks. Separated by the Eighth Street axis that visually links the pediments of the National Archives and National Portrait Gallery, the two new buildings mirror each other across the wide space. But for all of their grandeur they are welcoming -- they shape the space, envelop it, shelter it, like great cupped hands. And up above is the dome of sky for which the low city of Washington is justly renowned.

The directness and boldness of this architectural gesture makes up for a lot. In detail the Hartman-Cox version of classical architecture is quite dry -- not exactly copybook classicism, but close. There's none of the relaxed inventiveness and even whimsy that informs most of the neoclassical buildings of the Federal Triangle on the south side of the avenue. More fundamentally, one could argue that this was not the place for another neoclassical monument. The avenue, after all, is the dividing line between official Washington and the commercial downtown, the "unofficial" city. It was a situation that invited architectural differentiation, lively contrast between south and north.

But the succinct authority of the design sweeps away most doubts today, even more so than it did six years ago when the design was selected in a developer-architect competition organized by the Pennsylvania Avenue Development Corp. (PADC). It is by no means a simple design, and not so cohesive as it first seems: The classical colonnade, mimicking at long distance Bernini's forecourt for St. Peter's in Rome and, closer to home, the hemicycle in the Federal Triangle, disguises considerable complexity.

The challenge was indeed formidable. These buildings were given several different, even contrary, jobs to do. To conform to the PADC plan, they had to frame the circular memorial plaza, provide space for restaurants and stores on ground level, accommodate large-scale prestige office tenants and, not least, offer more than 200 residential units. The design accomplishes these various tasks ingeniously if not seamlessly.

In formal terms the least satisfying major elements of the design are the four residential floors, with their balconies and balustrades set back from and stacked atop the office buildings as on two identical wedding cakes. (The most visible material on the top floors, glass-reinforced concrete, reinforces this metaphor: It looks like painted cardboard.) But function takes precedence over form here. Providing the residential units with prime city views has obvious advantages from the standpoints of marketability and livability. In other words, this is an unfoolish inconsistency -- these condominium apartments (ranging from studios to two bedrooms, costing from $100,000 to $600,000) read clearly as apartments, not as mere extensions of the office buildings below.

A subtler shift in design takes place horizontally, at the point where the giant colonnade (13 50-foot-high columns per building) stops and the rest of the buildings begin. Materials change from limestone blocks to tan bricks, and the windows from metal and glass curtain wall to a paired double-hung sash pattern reminiscent of the old downtown. This is an adroit, appropriate mix of a commercial vernacular style with neoclassical pomp, held together by a continuous entablature and rusticated base.

Interior appointments of the main public spaces, designed by the Washington office of Morris Architects, a Houston-based firm, are about what one would expect: They're hardy, becolumned classicals. The office lobbies display rich materials in vulgar abundance -- mahogany panels, polished marble floors and columns, bright brass fixtures -- but, just two stories high, they're delightful in scale. Also delightful is their accessibility from both the avenue and side street facades. Basically, architectural attention is focused here on the exterior space, as more often it should be. Look, Mom, no atria.

What remains to be seen is how lively the outside space will become, but the prognosis is good. Sitting above a Yellow Line Metro station, it has location going for it -- this place is but a single block from the tourist attractions of the Mall and is the centerpiece of PADC's downtown residential quarter. It has good storefront design -- plenty of glass under attractive segmented arches. It has two corner restaurant tenants -- the 160-seat Peasant on the west, already open, and the even more upscale 701 Restaurant on the east, due in December.

And it has the Navy Memorial. Not the usual, passive monument, this one plays host to military band concerts on summer evenings and eventually will include a souvenir store, a "combat personnel information center" (both scheduled to open next year) and a 250-seat theater for "At Sea," a 23-minute flick modeled on the Air and Space Museum's gripping "To Fly."

(Still to come, incidentally, are the quiet plantings for the Eighth Street corridor, which, south of D Street, will be for pedestrians only. The tricky issue of what to put between the edge of the memorial and the new buildings is yet to be resolved. There were to have been identical glass canopies on either side of the memorial, but those were excised from the design, to its betterment -- as the project neared completion it became apparent they would interfere with the architecture.)

Above all, of course, the curiously named Market Square possesses that spectacular union of architectural image and urban form. Primary credit is due to the firm of Hartman-Cox (George Hartman, partner in charge, with Lee Becker and Graham Davidson) for its initial bright idea and the design skill to see it through to fundamentally fine completion. Those fluted limestone columns etched against the curved facades of metal and glass are indeed a sight to see.

Other credits include the PADC itself for the urban design idea of combining the buildings with the Navy Memorial in this way; the architecture firm of Conklin-Rossant for an excellent design of the memorial, after a bad start with an ill-conceived triumphal arch; the National Capital Planning Commission for sensibly saying no to the Navy Arch; and the Trammell Crow Co., the developer, which took over the project in midstream and had the sense to insist on high quality.