AN embassy chef, one would expect, would wear at least a white jacket; and for more-or-less public occasions he might wear a toque. But at the Finnish embassy the chef wears a Marimekko shirtdress, for Rauni Murtovaara-Nikkinen is one of perhaps only two women who are embassy chefs in Washington (the other is at the Danish embassy).

Murtovaara-Nikkinen looks like what used to be called "a mere slip of a girl" and is inclined to wear flowers in her blond hair. Nothing to indicate that in a single year she--with the assistance of Anna-Leena Holopainen, and occasionally a hand from Helena Iloniemi, the ambassador's wife--has cooked for 1,700 guests at the embassy and another couple of thousand at receptions outside the embassy. Once, admits Iloniemi, they did call in a caterer--but that was only because there were two luncheons the same day.

When Helena Iloniemi entertains, the food always includes something Finnish, and usually is handmade right down to the rye rolls. So what do these three women, who obviously love food . . . Finnish food . . . cooking Finnish food . . . do when they are not required to entertain? They plan another buffet lunch of typical Finnish foods to show off the cuisine one more time, before Ambassador Jaakko Iloniemi and his wife return to Finland April 30.

What's to show off?

Finnish food ranks right there with Greenland's as one of the least-known cuisines. Thus it makes an unexpected logic that some of Finland's most beloved dishes use ingredients that Americans know how to cook only one way. Take liver. Americans saute' it. Period. The Finns turn it into a light and delicate custard studded with--of all things--raisins, and accompanied by--curiouser and curiouser--lingonberries.

About those lingonberries. They taste and behave much like our cranberries, which of course we use only as a relish with turkey, although the adventurous stir them into muffin batter. In Finland lingonberries or cranberries can also be a dessert, the prettiest pink fluff of a dessert that is a dead ringer for strawberry mousse except that it has no cream, no egg whites, no gelatin, just farina and berries.

Then consider smelts. If Americans use them at all, they are likely to toss them in a deep-fryer. The Finns immerse them in cream and dill or bake them in a pie, a pie that not only resembles but is heavy competition for Russia's kulebiaka of salmon. Its filling is smelts and eggs and dill, which sounds familar if you know the salmon version. But its crust is made with potatoes in the dough, and the result is light and rich and flaky, both easier and more interesting than the usual puff pastry.

Whatever the dish, it usually has dill, one quickly learns of Finnish food. Dill, chives, salt and pepper are the readily available seasonings in Finland, explains Helena Iloniemi. But if the spice rack is narrow, that only puts more pressure on the imagination. Raisins and liver. Fish stuffed with prunes. Butter--or cream--and eggs combined as cold sauces, as salad dressings, as hot sauces, so that those familiar ingredients take on totally different textures. In fact, butter smooths everything. Melted butter with dill seems a staple; Helena Iloniemi suggests pouring it over the fish tart and even on the liver pudding. For a dessert of an enormous flat rectangular oven pancake, however, she switches to whipped cream. But then in Helsinki those long, cold winters burn up a lot of calories.

Leave out the butter sauce and these dishes suit a Washington spring. FINNISH LIVER CASSEROLE (6 to 8 servings) 1 1/2 cups water 3/4 cup uncooked brown rice 1 1/2 cups milk 1 large onion, chopped 1 tablespoon vegetable oil 3/4 pound ground liver (veal or beef) 1/3 cup corn syrup or molasses 1 1/2 teaspoons salt 1/2 teaspoon white pepper 3/4 teaspoon marjoram leaves, crushed 1/2 teaspoon ginger (optional) 1/2 cup seedless raisins 1/2 cup cream beaten with 2 eggs 1 teaspoon oil for the casserole Melted butter and lingonberry or cranberry preserves

In a saucepan cook the rice in water about 10 minutes. Add the milk and continue to cook about 8 to 10 minutes, stirring once in a while. Cover and let cook until all the liquid is absorbed. Cool. Fry the chopped onion in oil until soft and light brown. Let cool a bit. In a large mixing bowl combine the rice, onion, ground liver, corn syrup, salt, pepper, marjoram, optional ginger, raisins and egg-cream mixture. Mix well. Oil a 3-quart ovenproof casserole. Pour the liver mixture in and bake at 350 degrees about 1 hour. The top should be browned, but not burned. Serve with melted butter and lingonberry or cranberry preserves. FISH PIE (8 to 10 servings) For potato pastry shell: 1 1/2 cups butter 1 1/2 cups cooked and mashed potatoes 1 1/2 cups unbleached white flour 1 teaspoon salt For the filling: 1/3 cup uncooked rice 2/3 cup fish stock or water 4 hard-cooked eggs 1 to 1 1/2 bunches of fresh dill 2 1/4 pounds smelts or herrings, filleted if desired 1 1/2 teaspoons salt 1 teaspoon white pepper 1/2 stick of melted butter 1 egg, beaten Dill-flavored melted butter (optional)

In the fish stock, cook the rice for the filling. Mash the eggs with a fork. Chop the dill. Mix the ingredients for the potato pastry as quickly as possible to prevent it from becoming tough. Refrigerate until cold. Divide the pastry in two and roll out to form two circles, one slightly larger than the other. Line the bottom and sides of a deep 10- to 12-inch baking dish with the larger piece. Fill the dish with alternate layers of rice, fish, chopped eggs, dill, seasoning, and melted butter. Cover the dish with the rest of the pastry and brush with beaten egg. Prick lightly with a fork and put in a 350-degree oven for 1 to 1 1/2 hours. Line bottom of oven with foil in case of overflow. Serve it with or without dill-flavored melted butter. OVEN PANCAKE (4 to 6 servings) 4 eggs 2 tablespoons sugar 2 1/2 to 3 cups milk 1 teaspoon salt 1 1/2 to 2 cups unbleached white flour Strawberry preserves for serving

Beat the eggs and sugar well, until thick and foamy. Add the milk and salt. Stir in half the flour and beat well (the idea is to give the batter a firm structure so it can rise in the oven). Stir in the other half of the flour, and beat for for about 10 minutes. Grease well a 9-by-13-inch pan. Pour the batter into the pan and bake for 20 to 25 minutes at 425 degrees. The pancake will bubble and parts of it will rise; the top and sides should be brown, the insides still a little chewy. Serve warm or cold, with strawberry preserves.