A QUIET revolution in the White House is turning the heads of heads-of-state. It is being shaped by the well-kempt, fleshy hands of Roland Mesnier First Pastry Chef, sugar sculptor, artist in cream, carver of chocolate.

Mesnier, 38 years old, looks a solid sort and quiet except for the plaid shirts and jackets he favors. Born in Besancon, in France's Jura region, apprenticed at age 14, Mesnier has been molding and shaping doughs destined for governing bodies ever since. Paris' George V, London's Savoy, Bermuda's Princess Hotels, 18 medals and 22 years after he left home for his first kitchen, the White House called chef Albert Schnarwyler at the Homestead in Virginia, where Mesnier was working, seeking recommendations for a new pastry chef. One audition later Mesnier had the job as pastry chef and lone Frenchman in the White House kitchen, which now consists of executive chef Henry Haller (Swiss), assistant chef Hans Raffert (German) and first family chef Frank Ruda (American).

Such a well-fed and soft-spoken figure as Mesnier hardly appears a revolutionary. Besides, one would expect the hotels of Paris and London, as well as the mountains of Virginia, to lull one with tradition. And the ingredients of Mesnier's culinary revolution are as common as ultra-pasteurized cream, Baker's chocolate and standard butter.

But Mesnier is addicted to change. "If he served raspberry sherbet 30 days in a row," marveled Frank Ruda, "he would serve it 30 different ways." The day before, Ruda added, Mesnier had served tiny balls of chocolate mint sherbet in cookie shells in the shape of leaves, with chocolate spines, garnished with rolls of white chocolate. "Roland is inspiring," Ruda is prone to say.

"Mesnier is a genius," agrees pastry chef Ann Amernick, who has worked with him at the White House.

"It's terrific," Henry Haller says of Mesnier's flights of fancy such as pear and honey sherbet shaped into pears and set in baskets woven of pulled-sugar ropes as even as any real ones -- or more so. The baskets, 17 of them, were decorated with blown-sugar pears for a state dinner for Juan Carlos, King of Spain; it took Mesnier a full day to fashion just four baskets.

"This is the administration that will appreciate it," Haller, who has been executive chef since the Johnson administration, explained. "The Reagans like desserts a lot. It's important to them."

In fact, Nancy Reagan personally previews the entire meal for each White House state dinner, critiquing the garnishes, the sauces, the cooking itself. Often the Reagans are said to praise the desserts, and to ask for seconds. Mrs. Reagan has been known to eat even the sugar decorations from her plate.

Ronald Reagan is the one with the sweet tooth, and has often asked for three pounds of Mesnier's cookies to take to Camp David. Mrs. Reagan particularly likes hot souffle's, and Mesnier takes pride in inventing new ones such has his bourbon souffle'. Nothing ordinary for him: "We've never even served a raspberry souffle' in the White House."

"My pet peeve is chefs who don't change," insists Mesnier, using as an example those who always put everything on a bed of shredded lettuce. He loves to do research, and has invented a tool for forming sugar flowers so that cake decorators can buy them rather than make them. He plans to show his invention publicly in February at Washington's culinary arts show.

Mesnier's days and nights are pastry; after a full week at the White House he teaches a twice-weekly professional pastry course at L'Academie de Cuisine in Bethesda. The course covers all the basics, the classical pastries, before moving into new-style presentations. "It is always important to know which is the classical," Mesnier tells his students.

But for Mesnier himself, it is original and modernizedpresentations that occupy his imagination. Last summer, for instance, Mrs. Reagan asked for a sherbet on a fresh peach half. So he cut the peach partway through to make petals and wedged into the cuts pieces of plum, setting it then on a pool of plum sauce.

While nearly everybody was vacationing from the White House that summer, Mesnier and Ruda spent time inventing light dishes and new ways of serving them, their appreciative audience being White House decorator Ted Graber. For Ruda it became a friendly contest in which he kept trying to win the praise that Mesnier always gained so easily. Ruda made a vegetable terrine with chicken farce on tomato coulis, and it was, he said, a big hit. But the dessert got even greater praise. The same with Ruda's veal rolls with pine nuts. Then Ruda came up with a star: boned chicken leg stuffed with a moisaic of vegetables and a very light chicken-spinach farce made without egg binder, just raw chicken, seasonings, cream and well-drained spinach pure'ed in the food processor. He marinated, roasted and sliced the stuffed leg, moistened it with a lemon sauce. Ruda was asked to repeat the stuffed chicken legs for the lunch to honor Sandra Day O'Connor after her swearing-in as Supreme Court justice. But the luncheon's climax was Mesnier's dessert: large blown-sugar lemons, their tops cut off and their interior coated with white chocolate to look like the pith, then filled with lemon sherbet. Each top, with a bit of green stem and a sugar lemon blossom, was cocked on the side of a lemon.

Ruda, age 24, is built enough like Mesnier to look like a cousin, though he sports a tiny mustache and dark-rimmed glasses, and his accent is Pittsburgh rather than French. His enthusiasm for working at the White House shows in his key ring -- a shower curtain hook from a White House bathroom -- and a White House roof tile he employs as a trivet. But his greatest enthusiasm is for the work of Mesnier, with which he sprinkles his talk.

He tells of the floating island, a diet dessert Mesnier dreamed up for Mrs. Reagan, with pink-tinged raspberry meringues floating on a fruit pure'e, decorated with tiny fans of fruits. More and more, the desserts are fruits, sherbets, ice creams.

"They eat lightly when they have big problems," Haller has observed over the years at the White House. But even on an ordinary day, Nancy Reagan eats lightly -- fruit and perhaps an egg for breakfast, soup and a light main course such as cold poached egg or chef's salad for lunch. They eat small portions, and have already cut out the cookies that used to accompany lunch as well as the petits fours for small dinners. But unlike the Carters, the Reagans have not yet foregone dessert, which is still served at every meal.

And unlike the Carters, the Reagans favor small parties -- about 60 people -- and give a pastry reception only about twice a month, a coffeecake reception once a month. The Carters had big parties -- often for 350 people -- sometimes daily. The Reagans' parties have more hors d'oeuvres -- since they have restored hard liquor to the White House -- and fewer desserts.

"All the state dinners are about the same," Haller has said. But the desserts they are a-changin'. For years, at the Homestead before the White House, Mesnier has been known for his Christmas confections: marzipan snowmen and Santas, Santa cookies and leaf cookies with chocolate veins. His Christmas trees -- made of sugar pastillage, which hardens like shiny plaster of Paris -- balance tiny marzipan candles in even tinier marzipan holders. This Christmas the decorations are going to include chocolate pine branches with chocolate pine needles and pine cones.

Mesnier's most ambitious presentation so far was at the dinner for King Hussein of Jordan. Each of the 17 tables was served a marron bombe of green pistachio ice cream on the outside to represent the husk of the chestnut, and chestnut mousse inside. A wedge was cut out as if it had been partly peeled. And it was placed on a ring of ice with autumn leaves, lit from underneath. But the tour de force was the fuzz on the pistachio ice cream "skin." Each chestnut was studded with 300 pieces of blown sugar the size of a pen point. That's over 5,000 matching prickles of blown sugar. It even outdid the hazelnut bombes for the state dinner for Venezuelan President Luis Herrera Campins, which were garnished with marzipan squirrels and had floating in their sauce a mosaic of paper-thin almond brittle.

The home cook, Mesnier has suggested -- his being an artist with an understanding of the practical -- might make chestnut fuzz with a pastry bag and whipped cream. And, except for blown sugar pears and marzipan squirrels, here are some of Mesnier's White House dessert creations.

Pastry Tips from Roland Mesnier

* A touch of red coloring improves the appearance of chocolate desserts.

* In making pa te a choux -- cream puff dough -- if it is too thick to slide off the spoon, add a few drops of water rather than more egg, to improve the texture of the finished puff.

In glazing doughs with egg before baking, use just enough egg so that the brush does not stick to the dough. Tap it on with the brush rather than brushing it.

* When using a pastry bag, hold the tip high off the surface you are decorating, "so you can see where you're going." Hold bag and press with right hand, guide with left hand.

* When dipping pastries in caramel for a glazed coating, scrape excess caramel off against the edge of the bowl; most caramel coatings are too thick. Caramel must be made in dry weather, most readily in winter.

* For cream-filled pastries, flavor the cream well, because when there is a lot of cream inside, "It better be interesting."

* To lighten cream fillings, fold one part whipped cream into two parts pastry cream, although in summer using all pastry cream is less risky.

* To test the temperature of fondant, touch it to your lips; it should feel slightly warm. It should also be pourable, about the texture of egg white.

PETIT FRIAND CHAUD (15 to 20 servings)

Marinade: Bouquet garni: thyme, bay leaf, parsley wrapped in cheesecloth Salt and pepper, to taste 1 small carrot, chopped 1/4 cup salad oil 2 cups dry white wine

For meat: 1 small onion 1/2 pound of lean veal 1/2 pound of lean pork 1 pound puff pastry 1 egg beaten with 1 teaspoon water

Prepare a small bouquet garni by wrapping thyme, bay leaf and parsley in cheesecloth and tying with string. Place in bowl. Add salt, pepper, carrot, oil, and dry white wine.

Dice onion. Cut meat into fine julienne, place in bowl and sprinkle with diced onion. Marinate in refrigerator for 3 days. Remove meat from marinade. Dice finely. Roll out puff pastry about 1/4-inch thick. Cut round pieces of puff pastry about 2 inches in diameter. Brush egg-water mixture on the edges. Place meat in center and top with another circle. Press edges to seal. Brush with egg-water mixture. Make a small hole through the dough using a small knife. Bake at 375 degrees for 20 minutes or until dough is golden. Serve warm as cocktail hors d'oeuvres.

HONEY AND PEAR SHERBET (4 servings) 2 No. 2 cans (1 1/4 pounds each) pears, drained and pure'ed Juice of 1 lemon 4 ounces honey

Mix the above and put in an ice cream freezer for about 20 minutes or until hard.

PEPPERMINT AND BITTER CHOCOLATE SHERBET (4 servings) 2 cups of water 1 cup sugar 3 ounces unsweetened chocolate Few drops oil of peppermint

Bring water and sugar to a boil and let cool to about 100 degrees. Stir in chocolate until melted; if necessary, return to low heat. Add a few drops of peppermint oil. Put in ice cream freezer until firm.

BOURBON SOUFFLE (6 to 8 servings) 1/2 cup flour 2 cups milk 14 tablespoons sugar 1/2 stick butter, melted 1/3 cup bourbon 7 egg yolks and 10 egg whites Butter and sugar for preparing dish Bourbon souffle' sauce (recipe follows)

In a saucepan, mix together flour and milk. Add 10 tablespoons sugar and the melted butter. Bring to boil, stirring constantly. Remove from heat and allow to cool for about 5 minutes, then add bourbon. Stir in egg yolks one at a time. Beat egg whites to stiff peaks with 1/4 cup sugar and fold into the mixture. Grease the souffle' dish with butter and sprinkle with sugar (just a light coating). Fill the mold 3/4 full and bake at 375 degrees for 25 to 30 minutes. Serve immediately with bourbon souffle' sauce.

BOURBON SOUFFLE SAUCE (Makes 2 cups) 4 egg yolks 1/2 cup sugar 2 cups milk 3 tablespoons bourbon

Mix egg yolks with sugar. Bring milk to boil and gradually stir into egg-sugar mixture. Stir over low heat just until mixture starts to thicken enough to coat spoon, but do not allow it to boil. Add bourbon. Serve with souffle', spooning sauce over each serving.

FRUIT FLOATING ISLAND (6 servings)

This recipe must, of course, be made during mango season. It is included because it has been a low-calorie favorite of Mrs. Reagan.

Meringues: 1 pint fresh raspberries 1 cup sugar 4 egg whites

Fruit sauce: 1 cup white seedless grapes 1 cup fresh mango pulp 1 cup fresh pineapple 3 tablespoons honey Grapes, mango and pineapple slices for garnish

Put in blender 1 pint fresh raspberries with 7 tablespoons sugar (or substitute 1 box frozen raspberries, drained, and omit the sugar). Strain and cook until slightly thickened. Allow to cool. Stiffly beat egg whites with 9 tablespoons sugar and fold into raspberry syrup. Shape the raspberry meringue into egg forms and poach in simmering water 1 to 2 minutes. Remove from water and place on kitchen towel. In a blender pure'e grapes, mango, pineapple and honey. For each serving, take a round, flat dish, place some fruit sauce on the bottom and place the raspberry meringue eggs on the sauce and decorate with grapes, mangoes and pineapple. Chill and serve.

MARRON GLACE (8 to 10 servings) For pistachio ice cream: 10 egg yolks 1 2/3 cups sugar 4 ounces ground unsalted pistachio nuts 1 quart half-and-half 1 cup heavy cream Green coloring, if desired

Chestnut filling: 4 egg yolks 1/2 cup heavy syrup, boiling (made from 1/2 cup sugar boiled with 1/2 cup water until thickened) 4 tablespoons canned sweetened chestnut pure'e Few drops rum 2 cups heavy cream

For garnish: 8-ounce can chestnuts in heavy syrup Whipped cream for decorating Chocolate sauce for serving

Beat egg yolks with sugar and pistachio nuts. Bring half-and-half to a boil and beat gradually into egg yolk mixture. Return mixture to stove and stir over low heat just until it thickens enough to coat a spoon and leave a track when you run your finger down the spoon, but do not boil. Immediately pour mixture through strainer to allow air to cool it, and continue to cool it to room temperature. Add heavy cream. Color, if desired, with green coloring. Place in ice cream freezer for about 20 minutes or until firm.

Line two 8-inch round bowls with ice cream -- about 1-inch thick. Allow to firm in freezer.

To make the chestnut filling, beat 4 egg yolks, then gradually beat in boiling syrup. Beat until cool and fluffy. Add 4 tablespoons chestnut pure'e. Add a few drops of rum. Stiffly whip 2 cups cream and fold into the egg yolk mixture.

Remove bowls of pistachio ice cream from freezer. Break whole chestnuts into small pieces, reserving a few for final decorating, and sprinkle pieces in the bowls of pistachio ice cream. Fill center with chestnut filling, adding more pieces of chestnut as you go. Freeze for 24 hours. To serve, remove from molds and place the 2 half circles together to form a round. Decorate as a chestnut with whipped cream piped through a small tube to look like the fuzz of a chestnut. Garnish with whole chestnuts, and serve with chocolate sauce.