French Ambassador’s Departure Will Leave Void in Capital Party-Going : Politics: In Washington, as in Paris, de Margerie has become a synonym for French diplomat.

Next month, the French ambassador’s venerable chateau here will still flow with champagne and the ancient friendship brought during the American Revolution by the Marquis de Lafayette. The koi in the garden pool at the Tokyo Modern Japanese ambassador’s residence will continue to grow fat and fancy, and the sake will be poured as freely.

Even so, with the mid-month departure of the French and Japanese ambassadors, the parties and the people will be different in those bastions of embassy row.

If all goes as now planned, Nobuo Matsunaga and his wife, Yuriko, after 4 1/2 years here, will go back to Tokyo, where he will be an adviser to the foreign minister. Emmanuel de Margerie and his wife, Helene, are on their way to a split-level life between Paris and Gascony.

In the diplomatic world, nothing is as certain as uncertainty. However, Ryohei Murata, counselor at the Japanese Embassy here in the early 1970s and now vice minister in the Japanese Foreign Office, is the new ambassador-designate. He has been an ambassador previously to Austria and the United Arab Emirates.

De Margerie said that “there’s good reason to hope” that Jacques Andreani will follow him as ambassador extraordinaire and plenipotentiary to the United States.

Andreani is staff director for the foreign minister, an important position in Paris. He has also served as French ambassador to Cairo and Rome.

No matter how wonderful Andreani is--and de Margerie says that the diplomat has ably succeeded him twice before, as first secretary in Moscow and as undersecretary for European affairs in Paris--not a hundred champagne goodby parties will reconcile capital society to the departure of Helene and Emmanuel (called Bobby by all his friends since his English governess nicknamed him).

For in Washington, as in France, de Margerie has become a synonym for French diplomat. As were his father and grandfather before him, and as is Andreani, de Margerie is an ambassadeur de France, a personal appointment of the highest rank held by only five. He has represented his country twice in Washington, once as counselor (1970-72) and, since 1985, as ambassador.

It seems the de Margeries, a couple of immense style--he was once director of the museums of France and literally lived in the Louvre--have given or attended every black-tie cultural affair since they came here.

In 38 albums of pictures and clippings, the de Margeries have chronicled Washington’s evolving forms of social life, from the 1970s’ tradition of having 24 political leaders to dinner to the huge 1980s’ affairs with business and cultural as well as political leaders.

“There are still a few great hostesses, such as Evangeline Bruce,” said de Margerie, “but the large parties by institutions and organizations are far more common, and though glittering, the quality of conversation is not the same.”

De Margerie thinks that the National Gallery of Art is the leader in the new style of entertaining.

“The flowers and the food are perfect, and the guests fascinating,” he says.

Madame de Margerie prefers four to 10 for dinner but often must have the embassy dining room’s maximum five tables of 10 or one of 22. “The best number is more than the Graces and less than the Muses,” says her husband.

The Japanese Embassy residence, on the other hand, was built to accommodate massive entertaining.

In the past week or so the Matsunagas have used their ballroom-banquet hall for two dinners (with magnificent menus with two kinds of soup, sushi, tempura and teriyaki salmon), each for 80 senators, congressmen and American business people who came from New York, California, the South and the Midwest.

At a dinner honoring House Speaker Thomas S. Foley on Oct. 30, Matsunaga told guests that he had traveled to all 50 American states--”and 30 times to New York”--during his time here.

He said that Washington is a tough town, where it isn’t easy to establish close contacts.

“But I have no reason to think my successor will have more difficulty than I,” he said. “Both the United States and Japan must survive through cooperation.”

The de Margeries are being memorialized in Washington by the Friends of Vieilles Maisons Francaises with a donation toward the restoration of Salon Dore, an 18th-Century room from the Paris Hotel d’Orsay in the Corcoran Gallery of Art.

The donation is appropriate.

For the glory of France, Helene de Margerie has turned official residences in the Louvre and in Washington, London and Madrid into elegant, impressive and even comfortable places to live. So some years ago she told her husband, “When we retire, I want a small place near Paris--in good condition.”

Now they’re going to the Chateau Mazeres--19 bedrooms, four or five entertaining rooms, 500 miles from Paris--discovered by the de Margeries as a picturesque ruin.

“The roof had fallen in, leaving large holes to the sky in four places,” says de Margerie. “But we’ve repaired that. Next we put in the windows.”

They are doing much of the work themselves, with the help of a grant from the government. Helene de Margerie has scraped enough of one wall to see a 13th-Century mural underneath centuries of paint.

Their daughter was married there in great style. Like the Japanese Embassy, the chateau accommodated 80 for lunch--a few more than the Muses, but not too many for the de Margeries.