If the French Embassy is a Washington gastronomic pace setter, then we are moving back to the basics of good provincial French cooking. "No more baby vegetables," explained Helene de Margerie, the wife of the new ambassador, Emmanuel de Margerie. "Small potatoes, small carrots, tiny onions are one thing. But these miniature vegetables, they have no taste." As for the length of cooking of vegetables, "Asparagus should not be as hard as a morceau de bois (a piece of wood), soft but still vert craquant (crunchy green)."

Pur,ees have been overdone, too, explained de Margerie, who plans at least three dinners a week with from 24 to 100 guests with Francis Layrle, the first- class chef at the embassy residence. "A few years ago everything was pur,eed in at least three different colors. I like a good pur,ee of celery root but not to excess.

"In my youth a meal always consisted of meat, potatoes or rice and sometimes spinach. Today we use many different vegetables, not only potatoes. I like that better, and it is lighter."

Before each dinner the ambassador and his wife act as Layrle's guinea pigs. "Sometimes I remember dishes my mother's cook served. I describe them to Francis and he re-creates them."

Recently Layrle re-created a filet de sole Murat after de Margerie related how Napoleon's General Joachim Murat came to Maxim's late one night when there was no more food. He entered the kitchen, found some filet of sole, a few potatoes and artichokes and created for himself a new dish.

"My husband loves bouillons or soups at dinner, never at dejeuner. It complicates my life for the grand dinners we have at the embassy." A dinner hosted by the de Margeries always opens with soup, then moves on to fish, meat, salad and cold dessert. Tartes are reserved for lunch.

"Soup at lunch surprises me," says de Margerie. Yet once the de Margeries went to a three- star restaurant in Paris that did not have soup on the dinner menu. They politely excused themselves and left.

"We never serve cheese at dinner. It is just too heavy." Nor do the de Margeries serve cheese with salad, as is becoming the custom in America. "A good red wine tastes best with cheese. If you are eating a vinaigrette dressing on your salad, you can't taste the wine."

When de Margerie's husband was ambassador to England, cheese was often served after the dessert at English homes. "I didn't like leaving the table with the taste of camembert in my mouth. For the men it was okay; they were then served port, but the ladies were always excused before the port arrived."

While in England, the chef tried to serve the de Margeries a soup of frogs' legs. "I wouldn't allow it. For us, frogs legs are a delicacy but the English like to make fun of us by calling the French frogs." Virginian buffalo meat was another matter. When Layrle tried to introduce roast buffalo to the de Margeries, their first reaction was that he had just gone too far. Layrle tried it on them anyway. De Margerie was so delighted with the taste that she came down to the kitchen between courses to rave to the chef. TCold Tomato Soup with Basil Serves 6 3 cloves garlic 11/2 cups basil 2 tablespoons olive oil 4 pounds very ripe tomatoes,

preferably plum 1/2 teaspoon sugar 1/2 onion, diced 1 celery stem, diced 2 tablespoons chopped parsley 2 cups chicken consomm,e Salt and pepper to taste

Blend the garlic, basil and olive oil, setting aside a few sprigs of basil for garnish. Add to the tomatoes and simmer with the sugar, onion, celery, and parsley for about 1/2 hour or until the tomatoes have been reduced to three-fourths of their original volume. Add consomm,e to taste. Adjust seasoning, adding salt and pepper if necessary and serve cold, sprinkled with chopped basil.