It is hard to imagine a more challenging context for a new building than the stretch of Massachusetts Avenue NW known as Embassy Row.

There are few surviving streets on Earth where the architecture is so consistently elegant and yet so thoroughly varied. No single building is quite like another, and yet, for the most part, the ensemble is harmonious.

Richly harmonious. It took an extraordinarily wealthy and desirous clientele to pay for the superb materials, fine workmanship and architectural skills necessary to produce the splendid array. This happened long ago, in the first decades of the 20th century. Adding to such a distinctive, time-warped setting in the last decade of the century is at best a chancy proposition.

Nonetheless, it has just been done, and with considerable distinction. The new Turkish Embassy at 2525 Massachusetts Ave. NW is a handsome, smart addition to the distinguished neighborhood. It looks as if it belongs and, at the same time, it does not blend anonymously into the background.

The architectural character of the new building is intriguing--forceful yet relaxed, official without being stuffy. You cannot pinpoint a style. The building is a sort of period piece without a definite period, and while that definition sounds vaguely awful, the actual results, in the full light of the morning sun, look really good.

Ambivalence was built into the design. "The most important thing," says Patrick Burkhart of the Washington architecture firm of Shalom Baranes Associates, "was to achieve a certain sense of mystery expressive of East-West relations, a melding of two very different cultures. We didn't want it to be immediately identifiable as this or that."

The tactic worked. Americans will see a bit of 19th-century Italianate style in the two tower pavilions that are the building's most prominent exterior features. We will recognize echoes of Frank Lloyd Wright and early 1900s Prairie houses in the massiveness of the facades, the asymmetry of the composition and the emphatic, broad eaves.

Turkish citizens, on the other hand, are likely to discern reminders of certain 100-year-old streets in Istanbul or even specific structures in the capital city of Ankara. "When I first saw this embassy, I thought immediately of the First National Assembly building in Ankara," says embassy counselor H. Avni Botsali.

Fitting new buildings into sensitive urban contexts is pretty much a trademark of the Baranes firm. In the early '80s Shalom Baranes was one of the young architects equipped by training and temperament to negotiate conflicts between the city's tough 1978 preservation law and a commercial building boom downtown. Additions to the historic Southern and Homer buildings are among the firm's successes of that decade.

The Turkish Embassy shows the firm operating at peak contextual form. While looking at the finished building, you can almost hear the Baranes brain asking questions that turn potential obstacles into opportunities. Does Turkey's demand for office space threaten to overwhelm the avenue's residential scale? Are there certain conventions in the surrounding architecture we can use to make our office building better fit this environment? Are there elements in the embassy's program that we can exploit for expressive purposes?

Yes-yes-yes, come the responses. Much of this big building is underground. Divided into two pavilions with a hyphen-like glass-and-metal connector, the above-ground portion respects both the rhythm and scale of Embassy Row. The pavilions themselves correspond to the everyday and the ceremonial aspects of embassy life--the consular offices are located in the smaller, eastern tower, and the ceremonial entrance is in the larger, western one. (The line for embassy parties forms on the left.)

In other words, the architects got the big things right. What makes the building quite special, however, is that most of the littler things are right, too. The proportions of the towers and of window-to-wall (despite high security requirements) are intrinsically pleasing. The scale of the exterior walls is beautifully broken down from large to medium to small. Vertical is satisfyingly played against horizontal, positive against negative, solid against void.

And the materials are of a quality to match those of the earlier era--beautiful in themselves and beautifully put together. Inset panels, windows, piers, grilles, sills--the works--are expertly done in combinations of warm Kasota stone, iron-spot bricks and granites and slates of varying colors and finishes.

The abundance continues inside. Wood-paneled walls (on the ceremonial side of the building) and marble or slate floors in geometric patterns lead visitors downward. There is a huge, somewhat frightening bust of Mustafa Kemal Ataturk, modern Turkey's founding father, at the end of a sequence of stairs.

You turn right at Ataturk and descend again to the main ceremonial room with its high, vaulted ceiling--a rather graceful progression that almost disguises the fact that, to get to the main event, you have to go rather deep underground. Total disguise is impossible, of course. Baranes and colleagues squeezed in skylights at every opportunity, but many of the spaces (offices especially) inevitably suffer from that subterranean feel.

The Turkish government began planning the new facility back in the mid-'80s. The property sits in both the Sheridan-Kalorama and Massachusetts Avenue historic districts, and it took more than a decade of legal battles with neighborhood and preservationist groups before the Turkish government finally received permission to proceed with construction.

There is no question the new building is a squeeze. The hole in the ground for construction looked deep enough to accommodate the foundations of the Brooklyn Bridge. All the same, there is no disputing that the architecture of the new building is far superior to that of the modest town house that it replaced.

In researching the Turkish side of the architectural equation, Baranes, Burkhart and colleagues settled upon examples of a sort of hybrid style practiced by Turkey's first generation of European-trained architects. Combining Turkish vernacular elements with high-style European motifs, it was an attempt to develop an architecture that was at once cosmopolitan and distinctly Turkish.

There is a certain irony to the use of such precedents to build a contemporary Turkish embassy. After Ataturk's rise to power in the early 1920s, this first Turkish national style was superseded by an architecture more in keeping with his progressive, modernizing aims. Symbolically, a modern building in Washington might have been more appropriate.

But it would have been much, much riskier, and probably less wise. This particular site, hemmed in by buildings of extraordinary eclecticism and high quality, is extremely sensitive to change. The design by Baranes and company, with its skillfully interwoven strands, does honor both to Turkey and to this rare stretch of Massachusetts Avenue.