They stood there, the pair of them, with more diplomatic clout between them than you could count, and they smiled and they chatted and they pretended very carefully that they weren't posing.

Of course there may have been just a soupcon of exaggeration to the Gallic expansiveness of French Foreign Minister Jean Francois-Poncet as he talked away with Secretary of State Alexander Haig, but after all, there were, not six feet away, a dozen or so photographers snapping away, elbowing for position, lenses fixed on the stars of the evening, click, flash, snap.

Francois-Poncet is in Washington this week to test the temper of the Reagan administration foreign policy. Or, as he puts it, "one must have a sensitivity to what is here."

At last night's elegant dinner party at the residence of French Ambassador Francois de Laboulaye, Haig and his French counterpart appeared no less than best pals. A lot of laughing, a lot of friendly body language. And Francois-Poncet was heard to jest that "I've been trying to find something to fight about for two days, but haven't managed it yet . . ."

The American-educated (Connecticut Wesleyan, Tufts University's Fletcher School of Diplomacy) French minister is ebullient and voluble in both languages, sometimes at the same time. He switched briefly from discussing diplomacy to report that his 19-year-old son (one of three children), who is a student at the Sorbonne's Ecole Des Etudes Politiques, will spend this summer as an intern in the office of Sen. Charles McC. Mathias Jr. (R-Md.). Mme. Francois-Poncet, a slim blonde woman whose green eyes were reflected in her emerald silk Cardin gown, smiled happily that she was here "with no work to do, only for enjoyment."

The Haigs were the honored guests of the evening. Monday night it was the secretary and his wife who entertained the French mission and the visiting minister.

Jean Haig confirmed that they had found a house "just over the District line in Maryland." ("Westmoreland Hills," confided another guest.)

Armand Hammer, millionaire philanthropist, and outgoing World Bank president Robert McNamara were among the select guests. Also Mr. and Mrs. Richard Allen, President Reagan's national security chief; Secretary of Defense and Mrs. Caspar Weinberger, Special Trade Represenatative and Mrs. William Brock, former SALT ambassador and author Gerard Smith, Washington Post Co. board chairman Katharine Graham, and U.S. Ambassador to France Arthur Hartman.

From Capital Hill were: Sens. Clairborne Pell (D-R.I.); Charles Percy (R-Ill.), chairman of the Senate Foreign Relations committee; Sam Nunn (D-Ga.), James McClure (R-Idaho) and Paul Laxalt (R-Nev.).

"Laxalt," a diplomatic aide offered, "is really French, you know, on his father's side. Laxalt is a Basque name."

Rep. Clement Zablocki (D-Wis., chairman of the House Foreign Affairs committee) and Rep. and Mrs. William Broomfield (R-Mich.) were also present.

As guests sat down to a dinner of coquilles St. Jacques nage, noix de veau and glace nougatine, with three wines, an unusually large security force and embassy social personnel breathed easier. And back in a small cloakroom the Secret Service had made their own for the evening, a lone box of Nabisco Wheat Thins sat, starkly out of place in the Gallic opulence. And quite empty.