Pierre L'Enfant, in his 18th-century dream for Washington, saw embassies lining the Mall, an international promenade where the nations of the world would compete, not in war but in the art and architecture of their palaces. Instead, most of the diplomats of the early capital lived around Lafayette Square.

At the turn of the 20th century, Mary Henderson, the first of

Washington's women real estate tycoons, made magnificent plans for fantastic diplomatic mansions the length and breadth of 16th Street, which she called the Avenue of the Presidents. Such was her vision that even today some embassies still remain faithful to 16th Street.

The defection of the British to Massachusetts Avenue in the 1930s resulted in the establishment of 16th Street's grandest rival, Embassy Row. In those days, usually a single building sufficed for a chancery and an ambassador's residence. But following World War II and the emergence of Washington as the unofficial capital of the world, embassy staffs have proliferated.

The State Department has established an enclave for 24 chanceries across from the Van Ness Center and at a large site called Mount Alto on Wisconsin Avenue, just above Georgetown, for the Russians. Other chanceries are in office building sections of town, while some ambassadors have moved into posh residential areas. And recently some embassies have begun to construct new buildings that show off the art, architecture and culture of their own country. THE EMBASSY OF BELGIUM

The most grandiose residences, the true palaces, were often bought by foreign governments from that extinct species--the millionaires--who, before the Great Crash of 1929, built palaces in Washington for the winter high season. One of the most exquisite of these mansions, built in 1931 by architect Horace Trurmbauer, was originally owned by Raymond T. Baker, Woodrow Wilson's director of the Mint. The Belgian government bought the house in May 1945.

The drawing room (left) is furnished with Louis XVI chairs and settees, some covered in an Aubusson tapestry made in Belgium. Ambassador and Mrs. J. Raoul Schoumaker, who also have served many years in Asian countries, have given the house additional interest with their own Oriental collections. Over the mantel in the drawing room are jade carvings. A handsome mahogany table from China stands in the middle of the French windows, which form the west wall overlooking the garden. To the south of the drawing room is a paneled and carved library, full of leather-covered books, comfortable chairs and Chinese porcelain figures brought by the Schoumakers. THE EMBASSY OF KUWAIT

The Kuwait Embassy, on Tilden Street in Northwest Washington, belongs to the new fashion of ethnic embassies, which are designed in the idiom of the country.

The building is a duplex, with offices on the west side and the residence on the east. A handsome wall makes a hidden walkway between the two.

Baltimore architect Van Fossen Schwab designed the building in 1965, and notable embellishments were made by the then ambassador Talat Al-Ghoussein. To the atrium ballroom (left), he added an elaborate wooden trellis made of 27,000 pieces of walnut, put together by 18 workmen, under the vaulted ceiling. A small, low-ceilinged room next door to the ballroom looks like a westerner's dream of a harem room. The dark paneling comes from the Syrian Omayyed dynasty, circa 975.

A contemporary, sky-lit drawing room with a barrel ceiling is used by the present ambassador, Saud Al-Sabah, and Mrs. Al- Sabah for parties. THE EMBASSY OF TURKEY

Just off Massachusetts Avenue, on 23rd Street, stands the Turkish Embassy, built in 1915 in the Italian Renaissance manner. It has some of the most ornate wood carving and decorative painting of any mansion in Washington.

T he architect was George Oakley Totten, who designed 12 mansions that eventually became embassies. The original owner was E. H. Everett, who invented the crimped Coca-Cola bottle cap. The mansion was sold to the Turkish government in 1936 for $402,000. Embassy offices now occupy the ground floor, as well as an adjacent building.

The current ambassador, Sukru Elekdag, and his wife have recently had the carvings and paintings cleaned and restored in the elaborate entry hall and piano nobile. At the head of the stairs is a very large formal reception room and to its left is a drawing room. The dining room is full of heavy, carved paneling and beams with painted grapes and flowers. In the magnificent ballroom (left), with its stage and gilded mirror, the hand-embroidered 200-year-old silk has been dry cleaned and protected with silk netting by textile restorer Clarissa Palmer. THE EMBASSY OF ITALY

Firenze House and its 22 rolling acres on Albemarle Street were bought for $4.5 million by the Italian government in 1976. The romantic mansion is named after Florence, the mother of the late Robert Guggenheim. He and his wife, Polly bought the house in 1940. Blanche Estabrook Roebling O'Brien--of the Roebling family who constructed the Brooklyn Bridge --built the house in 1925. Russell Kluge designed the pseudo-Tudor stone mansion with the three-story-high baronial hall with its organ, the huge drawing room and about 50 rooms, if one counts the bowling alley, baths and utility space.

Ambassador and Mrs. Rinaldo Petrignani have filled their embassy home with paintings by Italian masters and with sculpture by modern masters. THE EMBASSY OF JAPAN

The most astonishing embassy residence in Washington was built by the Japanese on Nebraska Avenue in a mammoth effort that took five years and $12 million. Like the Kuwait Embassy, the Japanese ambassador's residence embodies the art and architecture of its country. But it reflects Japan, the new industrial giant, not Japan of exquisiste lacquer screens. The architect was the late Isoya Yoshida.

The great hall (left) has huge lavender crystal light sculptures by Tada Minami. The entire west wall of the hall is glass and overlooks the teahouse wing of the embassy and a carp-filled pond. Ambassador Yoshio Okawara and his wife have their own apartment and small Japanese garden within the 20- bedroom residence.