A young Harvard professor of old Bostonian lineage invited friends to a formal Saturday night dinner. After cocktails, the guests, attired in dinner jackets and long gowns, sat down to brown bread and Boston baked beans from an earthenware crock. Those who had attended dinners at his home before were not surprised. But to the uninitiated, the host explained: "Saturday evenings, my family always dines on baked beans."

The traditions of Boston cuisine have left their marks in many cookbooks and menus. But Washington, too, has its cuilinary traditions. Instead of turning to the region for inspiration, however, Washingtonians often look within. Nearly every home has a pattern: a particular meal that the family looks forward to eating on a particular night of the week. And as entertaining becomes less formal, many families stick with their favorite evening meal and serve it, and the occasional guest should expect no break in this pattern to suit his dining pleasure.

Call Monday self-righteous night. To start the week fresh, many of us prefer to eat a virtuous meal of meat and vegetables before retiring to attend to bills and to getting a good night's rest. Tuesday and Wenesday are casual nights, with relaxed menus often aided by home freezers, microwave ovens and the proliferation of gourmet carryout shops. Pasta has become popular as the base of such meals and is often topped with affordable amounts of meat or seafood to dress up the dish.

Generations ago, Thursday and Sunday were the cook's days off. This left the householder to create a simple one-pot meal like beef stew or Welsh rabbit. Now Thursday has taken on a special significance in entertaining because it is often the last night of the week in town for those who go to country homes or weekend retreats. But what better way to start the weekend than with a relaxed evening meal, in the fashion of the cook's night out?

Friday and Saturday remain, however, the big food nights for entertaining family or friends. These are the meals that require advance preparation and hours spent in poring through recipe files and cookbooks for that special dinner.

This leaves us with Sunday -- the day of the week in which family tradition plays its strongest role. Whether it's bagel and lox brunches, after-church roast beef lunches or Sunday evening stew, the food often is part of one's background and of one's culinary identity. What better time to share who you are with your friends than a leisurely Sunday afternoon or evening?

So relax and dish out for your guests what's already simmering on the back of your stove. In my family, that almost invariably was a gently bubbling stew with an aroma that -- along with the perfume of just-baked whole wheat bread -- wafted its way through the living room as we pored over the Sunday newspapers or watched the afternoon football game. We did the stew something like this. Sunday Night Stew Serves 4 to 6 1 large onion, diced 1 clove minced garlic 2 tablespoons butter or margarine 2 pounds chuck cut into 1 1/2-inch cubes 1 teaspoon dried thyme Salt and freshly ground pepper to taste 1 tablespoon Worcestershire sauce 1 pound carrots, peeled and cut into 1-inch chunks 4 medium potatoes, peeled, if desired, and quartered 1/2 cup red wine or to taste

Soften onion and garlic in the butter or margarine in a heavy casserole. Remove. Sprinkle the meat with thyme, salt and freshly ground pepper to taste and brown in butter. Add the onion and garlic and barely cover the mixture with water. Add Worcestershire sauce and wine. Simmer covered 2 hours or until meat is almost cooked, skimming off foam as necessary. Add carrots and potatoes and more wine and water if necessary. Simmer covered 30 minutes more or until vegetables are tender. Correct seasoning and serve with your favorite loaf of warm, whole wheat bread and a tossed salad.