In Washington, the Chronicler has noted that along with fund-raisers (political and charitable), book signings and annual dinners, arrivals and departures of potentates are the principal reasons for large parties.

So it behooves us all to remember the capital's unalterable rule: Say goodbye nicely to the Departing for soon again they may be the Arriving. Today's vice consul could be next decade's ambassador.

Yet seldom are farewells said with such flags, food, fanfare and frankness as the party Nuclear Regulatory Commission Chairman Ivan Selin and his wife, Nina, gave last week for 186 guests -- 12 ambassadors, four or five senators and assorted grandees -- wearing black tie and diamonds in the State Diplomatic Reception Rooms' Benjamin Franklin banquet hall.

The coming-and-going theme applied to both host and guests.

Selin is leaving the NRC to set up a business, Phoenix Energy, with his wife and son, Douglas. The company will explore building non-nuclear power plants in Southeast Asia. The elder Selins, however, will keep their headquarters here.

The Selins' honored guests, French Ambassador Jacques Andreani and his wife, Donatella, will be leaving the embassy soon. The other honorees, Japanese Ambassador Takakazu Kuriyama and his wife, Masako (familiarly known as Kiki and Mimi), have no plans to exit.

Kuriyama apologized jokingly for being honored without departing. "Hope you won't be disappointed we'll still be around," he said, despite the rumor that the ambassador and his wife were soon to leave. A large sigh of relief was heard in the city's social circles, for a select 200 or so guests monthly enjoy Mimi's salon, demonstrations of Japanese culture from tea ceremonies to the arcane calligraphy of shodo -- not to mention her hospitality to Washington charities.

Selin said the honored guests were chosen because France and Japan have "the two most complete, and in many ways most interesting, nuclear power programs in the world, after the American program. . . . The French have two kinds of reactors and hundreds of kinds of cheese, whereas in the United States the figures are reversed. The Japanese have set standards for construction efficiency and operational reliability that are the envy of the world."

Selin has served under four presidents (equally divided between Republicans and Democrats) in august positions in both Defense and State, with a profitable interval as founder of American Management Systems. Money from the latter stint, he said in response to a rude question from the Chronicler, paid for the party. "NRC's budget has been cut," he said. "We have no money for parties." Though the Selins picked up the tab, he said the dinner was "official" -- with a color guard and the Army Chorus. Andreani and Kuriyama first came to Washington as young foreign service officers, years before their return as envoys extraordinary and plenipotentiaries.

After the dinner, Andreani told the Chronicler that the date of his departure and the identity of his successor have not yet been settled. Nor does he know for sure what he'll be doing back in Paris -- "consulting, writing, keeping up with our American friends -- all those things," he said.

Donatella Andreani, like many diplomatic wives, looks forward to once again practicing her profession. The simultaneous interpreter said, "I have kept up with my colleagues."

Washington charities will miss her enthusiasm and expertise as a simultaneous American-French fund-raiser. Dressed in the best French fashions, she has entertained to benefit the Vieilles Maisons Francaises and Societe Generale, which helped the Corcoran Gallery of Art restore its famous French Salon Dore; the effort that moved the statue of Joan of Arc to a place of honor at the 16th Street entrance to the Meridian Hill Park; and Woodrow Wilson House events commemorating the World War I armistice.

The adieu and adios have another use. The departing diplomat may offer some thoughts -- usually diplomatically put -- about the United States.

Andreani told guests, "If you have invited us so gently in this very intimate ambiance, it is because we will know soon the normal fate of the diplomats: moving, and in this case, moving back home." He spoke of their five-year posting as "full of exciting discoveries, fond memories, passionate debates, beautiful and lasting friendships."

However, he said, when the United States disagrees with France, there's more fuss about it than if "any other allied or friendly nation happens to disagree with you.

"Arrived at the last moment of my career," he concluded, "I can admit that we happen to be wrong at times, but we like to defend our point. . . . We are very much part of this globalization of the world economy, but we will not cease soon, I think, to be the country with 300 sorts of cheese." CAPTION: Traveling in diplomatic circles, from left, are Masako and Takakazu Kuriyama, Donatella and Jacques Andreani and Nina and Ivan Selin.