Open Monday through Thursday, 8 a.m. to 10 p.m.; Friday, 8 a.m. to 11 p.m.; Saturday, 9 a.m. to 3 p.m. and 6 to 11 p.m. No credit cards. Reservations at dinner only. Prices: Weekday main courses $4.75; Saturday evening main courses average $6.50 to $7.50.

BULLETIN boards are hung with 2,000 of its menus. Weekly schedules are planned around the alternate-Thursday couscous or the alternate-Tuesday choucroute. The coffee break has gone grand as colleagues and neighbors gather over brioches and croissants. And 19th Street has the Parisian touch of baguettes being carried under seersucker-clothed arms.

The Bread Oven is insinuating itself into the habits of Washingtonians.

One wonders what could seem new on a street lined with the Apple Tree, the Palm, Pierce Street Annex and Flaps. One wonders until one gets the drift of The Bread Oven - boulangerie, patisserie, coffee bar and restaurant, with long and round French breads being disgorged from bigh French ovens in the dining room, with cherry-glazed ducks and mouses de foie nudging pastry swans in glass cases. These are the temptations of the takeout counter. As for the restaurant area, it is a kaleidoscope that changes through the day.

8 a.m. - The first wave of lawyers and other bon vivants, fresh from jogging, gather around window tables or pull up chintz-covered stools to the coffee bar. The display counters are piled with just-baked croissants, topknotted brioches, flaky apple turnovers and raisin danish. Self-service it is at breakfast, which creates the opportunity to wander from table to table picking up gossip along with the espresso. The Bread Oven has real cafe au lait, the milk steaming and foamy. It has cappuccino and hot chocolate, and you can choose from individually brewed coffees - 11 kinds - and teas - 10 kinds - at 75 cents a mug. The breakfast breads and pastries are good - too good for early-morning restrain - flaky where they should be and well browned and heavily laced with butter. Breakfast stretches on until . . .

11 a.m. - The lunch crowd starts lining up, the line moving fast to fill the round butcher-block tables, their ladder-back chairs tied with quilted chintz cushions. By now large-stemmed glasses are stuffed with bouquets of brown and beige linen napkins. The sun streams through ornately etched window walls to bounce off the glass-framed doilies and baroquely carved woodwork. But the focus in the menu, a complicated contract in which all main courses are $4.75. Every day the choice includes an hors d'oeuvre plate, a picturesque, if under-proteined, plate of zesty celeriac and beet salads, pickled vegetables, a couple of cubes of pate, an herbed deviled egg, a bit of king crab, and other assorted colorful bits of splendid vegetables. The same price buys, each day, a commendable small minute steak with authentic french fries, or a plate of cheeses of sterling character if not impressive volume for the price. Then there are the two daily specials, at the same price, one meat and one fish: Shrimps lightly battered and unctuous with lemon-parsley-garlic butter; couscous, a plateful of astonishing quantity, weighted with chicken, beef, carrots, turnips and chick peas on raisin-studded, cinnamon-scented cracked wheat. The rich flavor of the couscous was marred by dry meats and grains; another ladle of broth would have helped. On some days the fish choice is sea bass grenobloise, lightly battered and garnished with lemon bits, capers and tiny croutons, expertly cooked but the fish itself somewhat tired. Usually the fish has had more life to it; it might be trout with mushrooms and shallots, rockfish with eggplant, shrimp and tomatoes. As for the meats, one day it is blanquette de veau, another day cassoulet, another day ham with madeira sauce or pork with lentils. A sample of coq au vin was pleasant food, but the chicken was overcooked and the flavor of the thin sauce not absorbed by the meat. In other words, the main dishes vary from rather good to extremely good, as do the salads. Appetizers, on the other hand, have been consistently excellent, one day a cold salmon as soft as a mousse and sweetly fresh, with herbed mayonnaise. The lentil soup was hearty and boldly seasoned. A fish soup, creamy and rich, was as successful as the lentil, an asparagus ravigotte as refreshing as the salmon. Only the rillettes de porc, greasy and mined with bits of bone, was a disppointing beginning. Apetizers add about $1.75 to $2.75 to the bill. On Saturday nights the chef does more elaborate things - at higher prices - the likes of boeuf en croute and sole in champagne sauce.

Most important, the meal is framed with bread. A basket at the beginning of th meal disappears, it being chewy and glutenous as French bread should be, with a deeply brown crust that crackles between the teeth. With it, sweet butter. After it, a yen for more of it.

The wine list suits, being carefully chosen and reasonably priced, with several bottles at $5.50 and a house wine such as soave at $1.50 a glass. The service also suits, being energetic and congenial.

That brings the eater to dessert, or perhaps to considering afternoon tea for another day. Beauty lies in those glass cases, small frosted round gateaux, rectangles of cherry or strawberry tarts, cream puffs formed into swans and crowns. In The Bread Oven's early days, pastries were its weak link, but the pastry chef imported from France has been steadily improving (maybe one day he will even stop decorating his sophisticated little cates with chocolate jimmies). By last visit, the buttercream frostings were light and smooth, needing just a little more flavoring; the rum slice was moist and heavy with rum, larded with candied fruit and buttercream, glazed with almond paste and bittersweet chocolate. An eclair had not risen to its full performance, but its pastry cream was velvety, its crust eggy and crisp. To end the meal, the same proud coffees as at breakfast.

Dinner is a repeat of lunch, except on Saturday.The breads, pastries and cold dishes like pates can be bought to take out. And bring along your calendar to schedule your cassoulet day or your moules au chablis day.