BRILLAT-SAVARIN, who wasn't a cook, is remembered for his remarkable reflections on the art of dining.

Mary Henderson, who is a cook but almost certainly would shrink from being labeled a philosopher, has some noteworthy reflections on the art of entertaining with food. For example:

"Cooking books should be read for pleasure, tried out for pleasure and then the recipes should be adapted to your own taste. Whatever the dish is, it shouldn't be somebody else's. Make it your own.

"Food should be amusing and be a topic of conversation at the table. It should look attractive, be interesting and taste interesting.

"Avoid over-decoration. The decoration must not take too long because the dish deteriorates and the decoration must be part of the dish. Never decorate with anything you can't eat.

"To think rich in planning a menu nowadays is a mistake. To prepare complicated dishes that take away from the original taste of the ingredients is wrong.

"People really appreciate something original, a little bit new. If I serve fruit ice cream, I will have tiny little tarts made from the same fruit. sIt's sort of like dotting the 'i,' it reminds them what the ice cream's made of.

"I tend to do the opposite of what one should do. I treat the embassy like a restaurant and don't vary the menu all the time. Instead I serve specialities of the house.

"I have as much as possible done in advance, then the chef can concentrate on one special course and I can relax. Having to wait for food is bad and I'm afraid I haven't reached the stage where I can make charming conversation while biting my nails wondering what will happen next.

"The problem with official [embassy] entertaining is that it tends to be too formal. It would be more stimulating if each embassy tried to show its guests what dining in a fine restaurant in their own country would be like."

A final pensee from Sir Nicholas Henderson, the ambassador of Great Britain and Mary Henderson's husband: "We never see why entertainment should not be entertaining."

Diplomacy, as we all know, is meant to work in a slow and careful fashion. Diplomats, however, can make almost instant impressions by the force of their personalities. The great turnaround on Massachusetts Avenue in the past year has not involved world politics. Rather it has been the rapid emergence of the British Embassy as the premier table on Embassy Row. The meals Lady Henderson serves show the imagination, wit and taste to fully complement the lively conversation for which the embassy always has been noted and the magnificent setting.

People talk about being served miniature Scotch eggs resting in nests shaped from potatoes (they are quail eggs), deep fried pancakes shaped to resemble a purse with a surprise filling, a cold souffle containing another surprise -- hot lychees, an exquisite version of that English standby kedgeree, pear sorbet presented in the shape of a giant pear. They talk about the wines, choosen by Sir Nicholas as carefully as his wife chooses her recipes.

Lady Henderson herself mastered the British talent for understatement some time and several embassies ago. "I'm not a professional," she said one recent morning. "I cook because I love it and I'm delighted when things come out right . . . Food has been a major part of our official life. I started by cooking it all myself, then I began to teach our cooks to do things the way I like them."

When your embassy "cooks" have included a former chef to the duchess of Windsor (in Paris) and a former chef to the king of Greece (in Germany), it takes a lot of confidence in the way you like things to direct rather than merely accept. Lady Henderson, a soft-spoken woman, comes into a kitchen conflict armed with an impressive intelligence as well as humor. More important, perhaps, she has the sophisticated palate of one who has lived and entertained in more than half-a-dozen world capitals over the past 30 years.

She remembers the high quality of country cooking she tasted as a girl and can present "English" recipes without becoming the least defensive. ("I've tasted nothing better in my life than some plain English dishes.") So roast beef, game pies, vegetables such as Brussels sprouts and puddings, prepared with a light touch and never overcooked, are served to her guests along with English cheeses.

She also remembers life in Greece, where she and her mother were during World War II. "There was no money. The servants were gone, so I went into the kitchen and learned to cook with a book in my hand. Then came famine and we lived on a little wheat. I remember a 'Christmas pudding' that was a treat because it had a few raisins in it." Improvisation in the kitchen became instinctive. Later, at various posts, she created delicate moussakas, a scaled-down variation of the traditional baklava and other recipes. "I think I do tend to put a bit of the Mediterranean in my dishes," she said.

There are amusing memories, too: Of her Paris chef, who had "learned what perfection means from the Duchess of Windsor" and therefore didn't mind being asked to practice a dish two or three times to get it just right. Of the woman cook in Poland who couldn't read or write, but who could be guided by Lady Henderson's drawings of how the dish should look. One evening the wrong dessert appeared at a banquet in Warsaw. On inquiry later, Lady Henderson was told an elevator carrying the loyal cook and her ice cream creation had become stuck between floors. As the dessert melted, the cook shouted directions from her prison and the butler was able to present a substitute.

In Bonn, once, the delay before the first course was served became intolerable. What's wrong, Lady Henderson inquired. "I burnt the quiche," the chef responded. "So move on to the second course," she said without hesitation.

"What else is there to do?" she asked the other day with a composure she surely didn't feel that evening.

One thing, it turns out, is to hedge against potential disaster. The entertainment pace at the embassy here is heavy. Lady Henderson rattled off a week's program, which included a reception for 300, followed by dinners for 40, 60 and 40. Her chef, like the rest of the small kitchen staff, is English. He is Harry Simpson, a Londoner in his mid-20s who trained at Claridge's.

"At this point I have more experience in group entertaining than he has.I know what can happen at the last minute. So I type out the menus for each week, in rather a lot of detail if there is a buffet. I think first of what the chef can do in advance. I look for recipes that can be done for a lot of people and I know will work when we're in a hurry. If the first and last courses are done ahead, he can concentrate on the meat. Or if we plan an English game pie, everything but the top is done the day before so there is time to do a complicated first course at the last minute." Or dessert souffles with fruit sauce.

Although buffets are part of the way of life at an embassy, Lady Henderson dislikes the awkwardness and delay caused by long lines. Her solution is to create identical serving tables for each 10 guests. Another hedge: If there are four serving tables, she prepares five of everything. When all goes well, the food held in reserve is put to other uses.

A great many of her menus, plus recipes she used in Paris, have been gathered into a book. Published in France under the amusing title "The Cuisine Franglaise Chez Pauline" (The British embassy in Paris is the former home of Princess Pauline Borghese), it will come out in London this fall as "Mary Henderson's Paris Embassy Cookbook." American publication should follow next year. It is, Lady Henderson said, "a narrative with recipes written as I explained them to the chef."

One advantage Lady Henderson may have in her approach to entertaining with food is her sense of detachment. "I'm not a great eater," she said. "For myself I like best very lightly cooked vegetables and fish. I don't hanker after really rich food and I eat when we entertain to see if it is what I want it to be. Sweets to me are more like drawing something than creating a taste. I'm more interested in seeing their effect on the guests than eating them."

If Lady Henderson is a generous hostess, she is also a wise one. Her book will tell readers a great deal about the food she prepares and serves, but not everything. Take for example the dessert described as "The Chef's Williamine Pear." What is the recipe and how does he fashion the chilled ice into the form of a perfect pear?

"I'm afraid I'm not too keen to tell people that," says Mary Henderson. After all, a diplomat's wife has to have some secrets, too.

The comments on the recipes that follow are Lady Henderson's -- ingredients have been adapted to American measurements.

"Scotch eggs are a traditional British dish -- you find them in delicatessen shops an in pubs. But they are far beter made at home. They have the added attraction that you can have the children in the kitchen to help or even to do the whole dish, except for the frying. The method appeals to children as it is rather like playing with clay or shaping mud pies. The dish is excellent for picnics and cold suppers. We serve them cut in half (because it is prettier) for buffets and the method is used too for our quail eggs in baskets." SCOTCH EGGS (Makes 8) 8 eggs 6 large tablespoons of flour, sifted 1 teaspoon salt 1 pound port sausage meat 1 egg, lightly beaten 6 large tablespoons toasted breadcrumbs Vegetable oil for deep frying

Cook the 8 eggs for 10 minutes in simmering water. Remove shells and allow eggs to cool in cold water. When cool, roll each hard-cooked egg in the flour sifted with salt. Divide sausage meat into 8 parts, make a ball and flatten out. Place an egg in the middle of the pattie and fold the meat around the egg to cover to entire egg.

Coat all the eggs in this way, then dip the egg balls first into the flour again then into the beaten egg, and finally into the breadcrumbs. Roll each egg well each time so that it is well coated.

Fry the balls in a deep frying pan in hot oil, turning and allowing them to fry slowly until they are a rich golden color (about 4 minutes). Remove and drain. Cool and serve cold, slit in half and decorated with fresh parsley or watercress. We sometimes serve them as a first course with tartar sauce.

"Veal Belgrade is a dish I was served at the Hotel Metropol in Belgrade. The maitre d' hotel kindly gave me the recipe and we often serve it for small lunch parties." VEAL BELGRADE (6 servings) 1 pound fresh spinach 1 pound fresh green beans 6 small scallops (6 ounces each) of veal (chicken breasts or lamb chops may be substituted) Juice of 1 lemon 5 tablespoons olive oil Salt and pepper to taste 2 onions, chopped 3 or 4 green peppers, seeded and sliced 1 tablespoon of dried thyme or finely chopped dried mixed herbs 3 eggs 1 tablespoon freshly chopped parsley 1/2 teaspoon grated nutmeg

Wash spinach, drain and simmer wet for 5 minutes in covered pan. Take great care not to overcook. Drain well, squeezing out excess water and chop into large pieces. Prepare beans and cook in boiling salted water (about 10 or 15 minutes). Strain beans. Rub veal with lemon and about 2 tablespoons oil, sprinkle with salt and freshly ground pepper. But under grill or broiler and when crisply cooked, slice into strips. Heat oil, gently fry onions and green peppers, cover and simmer for 20 minutes, then add and lightly saute the remaining vegetables. Add the herbs and test seasoning.

About 25 minutes before serving, mix meat with vegetables and turn into an oven-proof dish. Beat eggs with parsley, grated nutmeg and a pinch of salt and pour over dish. Place dish in a 350-degree oven for about 20 minutes, or until top is golden brown.

"Ginger Crepes are a light and easy dessert. I think it is safe to say it was my invention and like most of the dishes the chef and I adapt, it looks more complicated than it is." GINGER CREPES (8 servings) Crepes: 3/4 cup all-purpose flour 2 eggs 3/4 cup plus 2 tablespoons milk Pinch of salt 2 tablespoons butter, melted Filling: 5 ounces (generous) sliced almonds 1/2 cup superfine or confectioners' sugar 1 1/2 ounces stem ginger in syrup* Juice of 1 lemon

*Available at specialty and Oriental markets.

To make crepes, place the flour in a bowl, add the eggs, cold milk and salt. Mix well and put through a fine strainer. The batter should be light and clear (add more milk if necessary). Add the melted butter and allow mixture to stand for 3 hours before cooking the batter in amounts just large enough to coat the bottom of a small greased frying or crepe pan.

To make dessert, fold the pancakes in two and cut into large strips about 3/4 inches wide. Bake the almonds in the oven until they are golden. Mix the pancake strips, the sugar, the ginger, the almonds and the juice of 1 lemon together very lightly. Serve warm in a warmed deep serving dish with a hot ginger sauce. Hot Ginger Sauce 5 tablespoons Lyle's Golden Syrup* 3 tablespoons water 1 tablespoon rum 3 tablespoons diced stem ginger in syrup 3 tablespoons superfine sugar

*Available at most Safeway and specialty stores.

Boil all ingredients for a few seconds and pour atop crepes.

"I once had this delicious tart in Barcelona and have used it as a first course and sometimes just cooked the spinach that way and serve it with roast beef." BARCELONA SPINACH TART (6 to 8 servings) Shortcrust pastry for a 10-inch pie or tart pan 3 pounds fresh spinach 1/2 cup plus 2 tablespoons sultanas 5 1/4 tablespoons butter 3 tablespoons all-purpose flour, sifted 1 cup hot milk 1/2 teaspoon nutmeg

Cook pie shell until lightly browned and keep warm. Cook spinach for 5 minutes in plenty of lightly salted boiling water in a covered pan. (About 1 heaped teaspoon of salt to 2 pints of water.) Drain (squeeze out excess water) very throughly and chop.

Make a bechamel sauce with the 3 1/2 tablespoons butter, flour and milk, then add the nutmeg and spinach. Heat up again, allowing spinach to boil for about 2 minutes. Heat remaining butter in a small pan and toss the sultanas and pine nut in this. Drain and then add the nuts and sultanas to the spinach and fill the warm tart shell with the mixture. Serve immediately.

It is essential to see that the spinach is well drained. You can add poached eggs (see below) on top of the tart allowing one for each guest if you wish. Sprinkle each egg with a pinch of freshly ground black pepper. Poached Eggs

Heat 2 pints of boiling water in a deep frying pan. Add 2 large tablespoons of white vinegar. Break the eggs one at a time in a cup and slide them gently into the boiling water. Allow them to boil for 3 minutes. The white film must be just solid enough to cover the yolk as the poached egg is, in fact, just a boiled egg without a shell.