ON CHRISTMAS Eve the Semler family is poised for the biggest feast of the year -- smorgasbord. This festive meal is a tradition that has been handed down for generations in Margot Semler's Swedish family.

While Margot is chief keeper of the smorgasbord she says, "if my husband didn't share, and I mean share equally in the cooking, we wouldn't be able to do it." But that is part of the tradition, too, because Margot's father was fully involved with her Swedish mother's three-week-long Christmas food preparations. "Mother and father did it together, as I hope our three boys will do. I would hate to see it disappear with us. We no longer start cooking as far ahead as we once did," she said. "We only really 'cook' for about three days before Christmas." Semler feels that keeping the family traditons is "in harmony" with her work as executive director of the National Cathedral Association.

"There are a number of things that Mother did that we don't do, such as cure our own ham; we buy one or make head cheese, we just don't care one way or the other about it. Sometimes we make pate, and sometimes we buy it. And we have eliminated some things too, such as cod paste. Cod paste made my children turn green when we merely opened it up on the kitchen counter. So the menu that remains is made up of the things that all of us really like: hot and cold meat and fish, salads and vegetables, breads, cheeses and desserts.

"We start at the German Deli on 11th street about 10 days before Christmas. When we are sure that Larsen's limpa bread is in the store we take our list. We also buy: 2 osts for the cheese tray (Swedish cheese somewhat like farmer's cheese), 1 with caraway, 1 plain; knackbrod (a dry bread similar to rye crisp); herring, fille knackbrod (a dry bread similar to rye crisp); herring fillets marinated in wine and dill; smoked eel; Swedish anchovy fillets in tins; fresh lingonberries. Everything in the store is so tempting. You can lose your mind in there, and your pocketbook."

Margot and Ralph Semler make "mounds and mounds and mounds of small Swedish meatballs, and gobs of deviled eggs, too. They disappear like peanuts."

When Ralph Semler brings out the aquavit in its ice cask and pours a drink for young and old alike, it's the signal for the feast to begin. Margot's sister Harriet Barlow gives the traditional toast in Swedish: Now the Christmas Spirit is come, Now the Christmas Spirit is come, Let us stop a moment and rejoice together. THE SEMLER FAMILY CHRISTMAS EVE SMORG ASBORD 1979 Buttered Nuts Liver Pate Smoked Eel Smoked Salmon with Lemon and Capers Shrimp and Eggs with Mayonniaise Souse Sillsalad with Sour Cream Sauce Herring Fillets Swedish Meatballs Jansson's Temptation Boiled New Potatoes with Dill Baked Glazed Ham Potato Salad Mixed Vegetable Salad Green Salad Stuffed Eggs Marinated Cucumbers Cheeses: Ost, Kummelost, Jarlsberg, Blue Lingonberry Tarts Aguavit Beer and Wine Limpa and Knackbrods Coffee and Mints Marinated cucumbers (6 servings)

Of the leftovers, the Semlers like these the best, in sandwiches of limpa and either ham and cheese or herring and cheese. 2 medium cucumbers 1/2 cup white vinegar 2 tablespoons water 1/4 cup sugar 1/2 teaspoon salt Dash of pepper 2 tablespoons chopped parsley

Wash cucumbers (do not peel) and slice thinly. Place in deep bowl. Mix vinegar, water, sugar, salt and peper throughly. Pour over cucumbers and sprinkle with parsley. Select a plate which will rest directly on cucumbers in bowl. Weight down and refrigerate about 3 hours before serving. JANSSON'S TEMPTATION (6 servings) 2 cups sliced onions 1/3 cup butter 4 cups raw potatoes, peeled and thinly sliced 1 can Swedish anchovy fillets, drained 1 cup half and half

Saute onions in 2 tablespoons butter. Butter a 2-quart casserole. Arrange a layer a half the potatoes, all the onions and all the anchovies. Top with remaining potatoes and dot with remining butter. Sprinkle with 1 tablespoon liquid from anchovy can. Add half and half. Cover with foil. Bake at 400 degrees for 30 minutes. Remove foil and bake 30 minutes uncovered or until potatoes are tender and golden brown. SHRIMP AND EGGS WITH MAYONNAISE SAUCE 8 servings) 8 hard-cooked eggs 3 cups shrimp, cooked and deveined 1 head lettuce Sauce: 1/2 cup heavy cream 1/2 cup mayonnaise 2 tablespoon chopped dill, chives and/or Parsley 2 teaspoon lemon juice 1 teaspoon salt Dash of pepper Cut eggs into quarters and arrange serving dish. Place shrimp on shredded lettuce eggs. Whip the cream. Fold in mayonnaise, dill chives or in a dish on the side. GLAZE FOR THE CHRISTMAS HAM

The Semlers apply this glaze for the last hour of baking. Then the family decorates the ham together, piping a framed "God Jul" on it with white frosting, and placing a paper bootie on the ham knuckle. "This glaze preserves the decoration nicely, says Margot Semler. 1 beaten egg white 1 teaspoon dry mustard 1 tablespoon sugar Fine dry bread crumbs (abaout 3 tablespoons)

Combine beaten egg white, mustard and sugar. Brush on ham, fat up, and sprinkle with bread crumbs. Bake at 325 degrees until nicely brown, about 50 minutes. LINGONBERRY TARTS (16 tarts) 4 cups lingonberries 1 cup sugar (or to taste) 16 baked, almond flavored tart shells (see below) 1 pint sweetened whipped cream

Boil lingonberries with sugar until soft. Taste and if too tart, (lingonberries are similar to cranberries) add more sugar and boil until dissolved. Chill. Fill tart shells with lingonberry sauce, cover with whipped cream and serve.

Tart Pastry: Add 1 teaspoon almond extract top basic recipe for two 9-inch double crust pies.