Dining and diplomacy go hand in hand. "When the roast appears and the wines begin to circulate," observed the 18th-century gastronome Grimod de la Reyniere, "tongues are loosened. That is the hour for declarations and demi-confidences."

Appropriately, Grimod's elegant Rue Gabriel mansion is an embassy today. Ironically, it's the headquarters of the nation that has bestowed the sloppy joe, the chocolate-covered marshmallow and the frozen TV dinner upon the world.

Rest easy, Grimod. When American Ambassador Arthur A. Hartman entertains formally, the food is firmly French. Only when the setting is more casual does the embassy offer its guests a taste of Americana. And even that taste is likely to be subtle. i

"In this city, you must serve sophisticated food," said Donna Hartman, a chic and slender woman in her early 50s. "If there is a sophisticated American cuisine, I don't know it. And if I knew it, I would not be capable of teaching it to a Portuguese chef."

So the heads of state and top-ranking diplomats who dine with the Hartmans might be served stuffed sea bass, flaming on a bed of fennel seed. Or aiguillettes de boeuf en croute (narrow strips of beef, larded, filled with mushroom duxelles and baked in crust). Or salmon quenelles . Or roast saddle of lamb a la Valencienne .

In fact, the only star-spangled main course served at a formal dinner since Hartman's 1977 appointment is Southern fried chicken. "It goes over very well," remarked an embassy staff member, "although it never seems quite fair to serve it, since they are not allowed to pick it up with their fingers. Etiquette, you see."

But one all-American dessert, pecan pie, has earned a frequent berth on even the blackest of black-tie menus. "French people like pecans; they don't exist here," said Mrs. Hartman. Still, she admitted, the pecan pie served on the embassy's eagle-crested china is considerably more continental than its prototype. It's flat, like a French tarte, with a lighter and flakier pastry than the standard American ice-water-and-Crisco crust.

On less formal occasions, Mrs. Hartman likes the food to flutter the flag, if not wave it. "All our buffets look like a typical American spread, with large American hams and turkeys. We've had pretty good success with chili con carne," she continued, "provided I get down to the kitchen to taste it as it's coming along.

"And," she added triumphantly, "we now have some of the world's great cookie chefs. Their chocolate chip cookies were a little too sweet at first, but a young American woman spent some time working with them in the kitchen and got it straightened out."

Mrs. Hartman personally plans the menus. Her kitchen staff numbers four: the Portuguese chef, his two French assistants and a dish washer. The large, professional kitchen -- its 26 copper pots hanging in strict gradation from miniscule to mammoth -- can produce anything from breakfast for two to a state dinner for 120.

The Hartmans usually spend Christmas and Thanksgiving in their Washington home, where their five grown children can easily congregate. When in Paris, however, the Hartmans celebrate American holidays with appropriate culinary flourish. The 1,500 guests at the ambassador's Fourth of July lawn party experienced such quintessential American treats as popcorn and ice cream cones.

But just how far the embassy's menus project an image of Americana isn't clear. One European diplomat here described the food at a recent buffet as "absolutely lovely -- though certainly not identifiably American. The eats and drinks were delicious, but they were international -- meaning basically French -- except for the odd American cookie."

In fact, sources report, virtually all the Western missions here serve French cuisine, perhaps with one or two of their own specialties. In contrast, Eastern embassies are more likely to offer their indigenous food.

Mrs. Hartman declined to speculate how well American delicacies please continental palates. But a French-born employe said she believes the food is an important eye-opener for Europeans. "They are the victims of the stereotyped notion that all American food is very sweet or very salty or hamburgers. So when they run across something like an excellent American smoked turkey, they are pleasantly surprised -- although I'm not sure they always like the cranberry sauce."

All social functions are held in the ambassador's official residence, which sits apart from the embassy and faces the fashionable Rue du Faubourg St. Honore. Built in 1842, the three-story mansion was once the home of the Baron de Rothschild and became a Luftwaffe officers' club during World War II. The U.S. government purchased it in 1948 and used it as an office building until 1971, "when it was decided that it deserved better -- and that the ambassador deserved better," as Mrs. Hartman puts it.

Mrs. Hartman said she serves the occasional sparerib for the same reason she has placed American artworks in the residence: It all helps create an atmosphere more in keeping with our national style.

The residence's 19th-century architectural furbelows and 18th-century furnishings create an aristocratic air. But the grandeur of the marble stairway is tempered by the wooden hyena from New Mexico, who sits among the plants at its base. And the gaze of the nymphs, sculpted in relief on the ceiling, seems directed at the patchwork quilt hanging on second-story walls.

Depending on the time of year and diplomatic climate, staff members say, the embassy may sponsor three social functions in a day or none in three weeks.

"But," emphasized one secretary, "you entertain because there is a reason to entertain -- a political meeting, a cultural event. The days are gone when you entertained for the splendor of the thing and invited "tout Paris."