THE PERILS of international politics being what they are, the annual Goodwill industries Embassy Tour isn't easy to put together. The threat of severing diplomatic relations, the imminent departure of ambassadors, the remodeling of quarters, the possible displeasure of special interest groups and often the impending arrival of the head of state-all can prevent an embassy from opening its doors.

Even so, every year the volunteers of the Goodwill guild-450 strong this year-manage to put together a tour, which probably attracts more people than any other. Muriel Threlfall is chairman under the honorary chairmanship of Rosalynn Carter. Some 3,500 persons, a third from outside of the Washington area, came last year.

The volunteers' most useful work is the compilation of information about the history and decoration of the embassies, which is published in the useful brochure that comes free with the tour.

(A definition may be useful: "Embassy" refers to a country's major properties. The ambassador lives in the "residence." Business is conducted in the "chancery," sometimes a modern office building. In some cases, these are combined in a single building. The Goodwill tour emphasizes the residences, the places you'll never see without a gilt-edged invitation or a Goodwill ticket.)

This year, the embassies of Great Britain, Greece, Netherlands, Romania, Sri Lanka and South Africa, as well as the Apostolic Delegation and the Textile Museum, will be open for Goodwill from 11 a.m. to 5.30 p.m. Saturday.

Most of the embassies are concentrated on Massachusetts Avenue, or nearby. At the turn of the century, when Massachusetts didn't progress much beyond Sheridan Circle, Mary Henderson tried her best to make 16th Street not only "The Avenue of the Presidents," but also "The avenue of the Ambassadors." She went down to defeat in 1931 when the British decided to build their imposing, if pompous, residence and chancery on Massachusetts Avenue instead. A great number of other embassies followed the lead.

The British chose Sir Edwin Lutyens as the architect. In the '30s, he was considered the greatest British architect.

The story goes that Lutyens planned the huge embassy to pretend to be an English country house, easier to believe then than now. So the style is pseudo-Queen Anne-the revival that brought forth the quip "a Queen Anne front and a Mary Jane rear."

Today, if you take a close look at some of the detailing of the house, you can see that Lutyens also stirred in a good teaspoon of art moderne flavoring. The 1930's detailing helped keep the mansion from seeming quite so ponderous and anachronistic. As it is, the massive building is the very image of what people think of when they say "embassy."

You come in through the great gates. It isn't easy to figure just where you should go from there, for the residence itself is entered through a porte cochere . The central portion is actually the offices. The statue of Winston Churchill, flashing the "V for Victory" sign (sometimes misunderstood by the younger generation) was sculptured by William M. McVey. It stands on the boundary between the British Embassy land and the District of Columbia.

The building is made of red brick, handmade in Pennsylvania in an effort to recall Tudor village bricks. The contrasting limestone pillars and pediments were quarried in Indiana.

The ground floor holds such service areas as the powder and cloak rooms. A great flying arch supports the twin limestone staircases sweeping up to the piano nobile or the main floor reception rooms.

The present ambassador, Peter Jay, and his wife have hung the walls with modern British paintings by Paul Huxley, Bernard Cohen, Robert Denny and others. Better take a good look; these represent the Jays' personal taste. They are expected to return home before long.

His library and study, paneled in red gumwood, is to the right at the head of the stairs. The 180-foot arched corridor itself is paved with black Pennsylvania slate and white Vermont marble, leading to a garden door at the west end. The banner of the Duke of Clarence, later William IV (1830-37), hangs now near the foot of the spiral staircase to the family quarters (not on view.)

The ballroom is the great room. The 40-foot long tapestry from Tabriz was designed for Queen Victoria's reception at the Crystal Palace in 1851. The chandeliers are Austrian, originally for gas. The mirrored walls are topped by a frieze copied from a Grinling Gibbons motif. The paintings come from the Tate Gallery, including an official painting of Queen Elizabeth II, two George Romneys and a Thomas Gainsborough. A neat touch are the marble busts of the opposing 18th-century politicians, Charles James Fox and William Pitt. Fox favored American independence.

The dining room almost seems small after the banquet hall. The furniture is walnut. The Sheraton china cabinet is especially fine.

The drawing room, also a more intimate space, receives its sparkle from the Chippendale mirrors left behind by Lord Lothian, ambassador from 1939-41. The Kirman carpet is woven with Persian poems and prophecies. The room, and indeed the embassy's chief glory, are the three Turner paintings: "Waves Breaking on a Lee Shore," "Venetian Festival" and "Morning, Returning From the Ball, St. Martino."

In contrast, in the glorious gardens is a large Henry Moore sculpture, called "Vertebrae," lent to mark the state visit of Queen Elizabeth II in the bicentennial year.

The netherlands Embassy was, like so many others, originally a grand Washington private home. The Owsley family (according to the tour brochure) built the house in 1929, when private owners could still afford the upkeep. The architect was Ward Brown, the builder Wilmar Bolling, a brother of Edith Bolling Galt (Mrs. Woodrow) Wilson. The Dutch government bought it during World War II. The family quarters are on the third floor with staff rooms on the top.

The state rooms are hung with tapestries and Dutch paintings, especially from the 17th century, including Aert van der Meer and Willem and Frans van Mieris.

The neo-classical embassy of the Socialist Republic of Romania also was once a private mansion, the home of Frank Ellis, originally of Cincinnati. Carrere and Hastings, a New York architectural firm, designed the house-as well as the Cosmos Club and the Old Senate and House Office buildings. The Romanians bought if from Franklin H. Ellis, the son, in 1921. They have made few changes.

The dining room and a small sitting room or office are on the first floor, off the marble-floored and colonnaded entrance hall. The principal reception room with its crystal lighting fixtures is on the second floor.

The Greek Embassy is the oldest on the tour, built in 1906 for Hennen Jennings, a mining engineer. The Greek government bought the property in 1937. Appropriately, the house has many Greek Revival touches, including late Corinthian and Ionic style columns in the inside.

Ancient Greek and Cypriot pottery and glass are displayed in the house, along with paintings by Alexander Alexandrakis, the brother of the ambassador, Menmelas Alexandrakis.

The Sri Lanka Embassy was built in the early 1950s. The Sri Lankans bought it from George A. Garrett, former U.S. ambassador to Ireland. Sri Lankan masks, used in devil dancing, hang on the staircase. Brass and silver work is displayed on many tables. A batik wall hanging tells a story of the Lord Buddha. A drawing of 1819 shows the procession at the king's palace at Kandy where the tooth relic was protected.

The South African Embassy, like the British, was built in 1937 for its current purpose. The facade is an imitation of the 300-year-old castle in Cape Town. According to the tour brochure, much of the inside paneling and furnishings are Ocatea Bullata, "called 'stinkwood' because of its pungent odor when fresh cut."

The Apostolic Delegation, the official residence of the papal representative in the United States, was built in 1939 to a Renaissance Roman design by Frederick Vernon Murphy. The paintings are largely religious.

The Textile Museum is put together from two buildings, the west building designed by Waddy Woon in 1908 for Martha Tucker. The smaller house was designed by John Russell Pope between 1913 and 1915 for George Hewitt Myers. The next year, Myers decided he didn't have enough space for his Turkish rugs and other textile collections, so he bought the Tucker house and joined the two, rather awkwardly, with a bridge. In 1925 the Tucker house was opened as the Textile Museum, the only one in this country. Now both buildings are used by the museum.

Tickets, $10 each, will be on sale at Goodwill stores and Ticketron before the day of the tour. On Saturday, the day of the tour, from 11 a.m. to 5:30 p.m., tickets will be on sale at all the embassies: Greece, 2221 Massachusetts Ave. NW; Romania, 2236 Massachusetts Ave. NW; British, 3100 Massachusetts Ave. NW; South Africa, 3101 Massachusetts Ave. NW; Apostolic Delegation, 3339 Massachusetts Ave. NW; Netherlands 2347 S St. NW; Sri Lanka, 2503 30th St. NW; and the Textile Museum, 2320 S St. NW. For information, call Mrs. Peter B. Johnson, 363-5960. CAPTION: Picture 1, The garden at the British Embassy, by Margaret Thomas-The Washington Post; Picture 2, British Embassy ballroom, by Margaret Thomas-The Washington Post