Like many Moroccans, Mercedes Ben Simon is superstitious, especially in the kitchen. For Rosh Hashanah, the Jewish New Year, she will not serve black olives or eggplants for fear that the color and sour taste might augur evil for the coming year.

As is the Sephardic and Middle Eastern Jewish custom, a prayer will be said over a number of symbolic fruits and vegetables prior to the festive meal which marks the beginning of two-day holiday on Sunday. First, sept legumes (seven autumnal vegetables) sprinkled with sugar and cinnamon will be boiled and roasted. Mercedes will serve pumpkin, zucchini, turnips, leeks, onions, quinces and Chinese celery. Before tasting the different vegetables her husband, Sam, will recite the following prayer: "May the coming year grow as a gourd in fullness of blessing. In the year to come, if enemies gird at us, mayest Thou guard us as we eat of this gourd with the prayer: Blessed art Thou, Lord our God, Ruler of the Universe who createst the fruit of the earth."

Other prayers, wishing for a happy, sweet, plentiful and prosperous year will be made both nights over dates dipped in seasame and anise seed and powdered sugar. The first night an apple will be dipped in honey and the second night the pomegranate will be blessed. Most important is the head of a fish or lamb served to the head of the family at the table.

After this short ceremony, Mercedes will serve a festive dinner in her Chevy Chase home, beginning with a blessing over pain petri , the sweet Moroccan challah with seasame and anise seeds. This will be twisted into a circle for a full round year.

The meal will continue with a pescado blanco , a baked whole fish in tomatoes and garlic. At Rosh Hashanah, according to Mercedes, it is important that the fish be white and that the head be attached.

Vegetable soup and the famous Moroccan pastels , meat-filled turnover, will follow. The main course will include a tongue with green olives and a green salad. Honey-dipped cigares filled with ground almonds and a hot mint tea will conclude the meal. Today most cooks buy phylo dough or egg roll wrapper for pastels and cigares. Mercedes makes her own dough.

The following day, after Rosh Hashanah morning services, Mercedes will serve a traditional Moroccan couscous with a sweet vegetable dish and a fruit salad for dessert. The second night her meal will include a variety of colorful salads and lamb with prunes and almonds.

Unlike Eastern European Jews who 10 days later break the fast on Yom Kippur (the Day of Atonement) with honey cake, Mercedes will serve tea and fijuelas , deep-fried pastries soaked in a sweet syrup.

What makes her dishes so very unusual is the combination of ingredients and recipes she uses. Inherited from her forebears, who fled from Spain at the time of the Inquisition, they have been modified to utilize the Middle Eastern foods that were available to her in Morocco and the American ingredients she uses today. Mercedes' own creativity adds the French touch.

Many of the foods served remind Jews of their Mediterranean origins quoted in Deuteuronomy: "For the Lord thy God bringeth thee into a good land, a land of brooks of water, of fountains and depths that spring out of valleys and hills; a land of wheat, and barley and vines, and fig trees, and pomegranates; a land of olives, oil and honey."

Moroccan women are fiercely proud of their culinary skills, with good reason. It takes both dexterity and extreme patience to prepare the dainty pastels and other delicious foods served at their holiday meals. Here are some of the recipes for the dishes Mercedes Ben Simon will prepare this Rosh Hashanah. MEAT PASTELS

(Makes 50 Pastels - 3 per person) 1 package fine egg roll wrappers (50 wrappers) 2 pounds lean ground meat 1/2 cup fresh parsley 1 cup grated onions 1 teaspoon mace 1 teaspoon nutmeg 1/2 teaspoon allspice 1/2 teaspoon salt 2 cups water

Vegetable oil for deep frying

One hour before commencing remove egg roll wrappers from freezer. Saute the ground meat over low heat, stirring occasionally. Add the parsley, onions and seasonings. Blend well and gradually add the water. Cover and simmer, stirring occasionally until the water evaporates and the meat is very soft, about 1 hour.

Place the meat in a food processor or put it through a meat grinder until it is smooth.

Cut an egg roll wrapper in half, then fold lengthwise.

Take one tablespoon of filling and place at one corner of the wrapper. Fold the corner over into a triangle and fold up like a flag. Place the last fold on the bottom. Repeat until all the wrappers are filled.

Place directly in the freezer for later use, or finish cooking immediately.

Heat 4 inches of oil in a heavy-bottomed pan to 375 degrees. Deep fry a few pastels at a time, turning when golden. Drain. Before serving place in a warm oven to heat through. GINETTE SPIER'S SWEET VEGETABLE DISH (8 to 10 servings)

Note: This dish is a typical Moroccan accompaniment to the couscous served at midday of Rosh Hashanah. It would also be a delicious vegetable dish served with a pot roast or roast chicken. 4 large onions, sliced thick 2 tablespoons oil 1/3 cup dried chick peas, soaked overnight 1 pound acorn squash, pumpkin or carrots 1 or 2 sweet potatoes or yams 1/4 to 1/3 cup raisins 1/4 cup sugar 2 teaspoon cinnamon

Saute the onions in the oil until golden. Grease an oblong casserole. Then place the chick peas at the bottom, cover with the onions, squash, pumpkin or carrots, sweet potatoes or yams and raisins. Sprinkle with the sugar and cinnamon and add a little oil if desired.

Baked at 400 degrees oven for 25 minutes or until well browned. ROSENBLAT's FIJUELAS

Moroccan deep-fried pastry to break fast of Yom Kippur. (Makes 24) 1 cup warm water 2 egg yolks 2 tablespoons vegetable shortening or margaine 1 teaspoon salt 4 cups all-purpose, unbleached flour Vegetable oil for frying 2 cups sugar 1 cup water 1 teaspoons orange blossom water Cinnamon

Combine the water, egg yolks, shortening and salt. Gradually add the flour, kneading gently as you go along. Knead until dough is firm, about 10 minutes. Cover with a towel and let rise for 1 hour.

When the dough has risen (it will not rise very much), break off a piece the size of a plum and flatten it out with the palm of your hand. Shape into a rectangle and roll it out in strip approximately 3 inches by 9 inches. It is easiest to use a pasta machine for this. Otherwise, use a rolling pin. The dough should be rolled as thin as pasta. When it is thin, stretch it out gently with your hands. Flour a cookie sheet and place each piece of dough on the sheet. Cover with a towel while making the rest. Continue until all the dough is used up.

In a heavy casserole, prepare oil for deep frying, heating it to about 375 degrees. With a slotted spoon place one end of the thin strip in the oil. As it cooks, it will roll up like a jelly roll. When the fijuelas are golden brown let drain on the side of the pan. Drain again on a paper towel. You must work very quickly cooking and draining so that little oil is absorbed. Continued until all the pieces are completed.

Combined the sugar and water and boil until a syrup is formed. Add the orange blossom water. Let cool to lukewarm. Pour the syrup over the fijuelas and sprinkle with cinnamon. If covered, the fijuelas will last several weeks. CIGARES

Fried "cigar" pastries filled with almonds. (Makes 50 cigares) 25 egg roll wrappers 3 cups blanched ground almonds 2 1/2 cups sugar 1 egg 1 tablespoon orange blossom water Grated rind of 1 lemon 2 cups vegetable oil or more 1/2 cup water 2 tablespoons honey

One hour before commencing, remove the egg roll wrappers from the freezer. Then cut each in half. Combine the almonds, 1 1/2 cups of the sugar and the egg. Mix well and add the orange blossom water and the lemon rind. Combine well. Place 1 heaping teaspoon of the filling in the center of each wrapper and roll up like a jelly roll. Moisten the ends to secure.

Fill a heavy frying pan with four inches of oil. Heat the oil and drop the cigares in a few at a time. When they are light golden, turn and then drain immediately.

Meanwhile, make the syrup. In a small, heavy saucepan bring the remaining one cup sugar and 1/2 cup water to a boil over a high heat, stirring until the sugar dissolves. Add the honey. Cook briskly, undisturbed, until a small bit dropped into ice water immediately forms a soft ball. When the syrup cools to lukewarm dip in the cigares. Drain off the syrup and place on a platter. L'AGNEAU AUX PRUNEAUX ET AUX AMANDES (Lamb with Prunes and Almonds) (8 to 10 servings) 2 pounds chopped onions 1/2 cup plus 2 tablespoons vegetable oil About 3 1/2 cups water 2 tablespoons honey 1 teaspoon cinnamon 16 shoulder lamb chops (2 per person) 2 pounds prunes which have been soaked in water 1 hour 1/2 pound blanched almonds

Cook the onions in 1/2 cup oil over low heat, stirring occasionally, until they are tender, limp and almost black, about 1 hour. Combine with the honey, cinnamon and sugar. Set aside.

Using the additional 2 tablespoon oil, saute the shoulder chops until golden. Then add 1/2 cup water, cover and simmer over a very low heat for 1 1/2 hours until the meat is very tender, stirring occasionally. Add more water when necessary to moisten. Add the onions with the soaked prunes to the meat and simmer, covered, 20 minutes more.

Toast the almonds and just before serving sprinkle over the meat. PAIN PETRI (Sweet Kneaded Bread for the Sabbath) (Makes 5 loaves) 3 pounds unbleahced flour 1/2 cup sugar 3 eggs plus 1 yolk 1/2 cup vegetable oil 1 tablespoon sesame seeds 1 tablespoon anise seed 2 packages fresh yeast 1 cup warm water 3 cups water

Place the flour in a huge bowl. Make a well in the center and add to the well sugar, 3 eggs, vegetable oil, sesame and anise seeds. Proof the yeast in the warm water. Then add to the well.

Using hands, gradually work in the flour with the ingredients in the well. Add more water as needed (about 3 cups). When a medium dough is formed, knead on a wooden board for about 20 minutes.

Form the dough into a ball, turn in a greased bowl to coat the surface and cover with a towel. Let rise in a warm place for 30 to 40 minutes or until doubled in bulk. Punch down and knead once more. Divide the dough into 5 pieces. Either shape into a round ball or make a long piece out of each and twist into spiral with the end of the dough at the high point in the center. Cover for about 1 hour and let rise until doubled.

Remove the dough to a cookie sheet covered with aluminum foil; brush with the remaining egg yolk and a tablespoon of oil and bake at 400 degrees for 1 hour or until golden. SALADE DE CAROTTES (8 to 10 servings) 2 pounds carrots 3 cloves garlic, minced 2 teaspoons paprika Hot pepper sauce to taste 1 tablespoon cumin 1/2 cup lemon juice or wine vinegar 3 tablespoons olive oil 2 tablespoons fresh parsley

Peel carrots and boil in water, about 20 minutes or until they are tender.Cool and cut in thin slices. Place the carrots in a mixing bowl and add the remaining ingredients except the parsley.Cover and refrigerate until thoroughly chilled. Before serving sprinkle with parsley.