Open for lunch Tuesday through Friday, 11:30 a.m. to 3 p.m.; for dinner Monday through Saturday, 5:30 to 11 p.m.; Sunday, 5:30 to 10:30 p.m. AE, BA, MC. Reservations.

Food: French, improved, but with some distance to go

Style: Beautiful eighteenth - century townhouse with second-floor terrace

Price: Lunch dishes $4.25 to $8.75, with fixed-price lunch at $6.95; dinner main dishes $7.95 to $12.95.

CONSIDER this a progress report, and hope for more progress. Jour et Nuit is under new management, and the signs are encouraging if not yet cause for full celebration.

The second floor and former living and dining rooms of an early Georgetown townhouse that belonged to an early governor of Maryland, Jour et Nuit would probably draw diners even if it served no food at all. The terrace, glassed in so you can eat there year round, is an undeniably delightful place to dine. And inside, eating in a graceful eighteenth-century room with a working fireplace is an experience that has drawn a certain faithful following through the restaurant's ups and downs. Now the interior has been redecorated with a muted red wallpaper and freshened with baskets of flowers on the deep-set windowsills. The terrace, already charmingly set with fan-folded pale blue napkins and fresh flowers, is being redone. With well-spaced tables in the three small rooms, Jour et Nuit feels as close as any restaurant to dining in a home, and that home is prettier than ever.

The stumbling block has been the food, but that, too, has undergone some renovation, especially at dinner. The printed menu is not particularly elaborate or original, consisting primarily of three sole dishes, two trout dishes, ten kinds of steaks, three kinds of veal, the inevitable duck a l'orange and rack of lamb. More interesting are the daily specials, such as rack of veal in cream or pheasant. And samples from among the specials found them indeed worthy of investigation. An individual rack of lamb, for instance, was delicately pink and perfectly trimmed, sauced with a tart, boldly herbed bearnaise and handsomely presented with a bouquet of fresh broccoli, grilled tomato, browned potatoes and baby carrots. Lobster, too, was cooked to just the right point, stuffed with lump crabmeat and sauced with a highly seasoned and highly buttered cream, glazed and golden. With a plate of carefully peeled and firmly cooked fresh asparagus vinaigrette and a robust, agreeable terrine de volaille garnished with cornichon fans and olive-centered cherry tomatoes, Jour et Nuit did itself proud. Given some good buys at the low end of the wine list - including a Pommery champagne at $15 - dinner there these days can certainly live up to its setting. And the white-jacketed waiters attend carefully without hovering, pace the meal well, present the dishes proudly before they carve. If you end with cheese - ripe brie and Muenster with a fan of apple slices - and give it time to warm to room temperature before you tackle it, or with strawberries in Grand Marnier and very good cafe filtre, you will have spent about $35 a person with tip, but life will seem delicious indeed.

Now for the bad news. A lunch of overcooked, dry salmon in a bearnaise that too much tarragon made cloying. What happened to that conscientious fish cook, that sensitive saucier who had been on duty at dinner? Rabbit in wine sauce was a generous idea and was served in a generous portion, but the meat was wasted in a thick, acrid sauce with oil oozing from its pores. There is safety at lunch in an omelet - large and puffy, sufficiently runny - and in a crab crepe, unless you object (as I do) to frozen king crab. You could make do with the terrine de volaille or the elaborately pretty hors d'oeuvres plate, and the clams casino are deliciously zesty with lemon and garlic. But the temptation is to order the $6.95 fixed price luncheon, on which the soup and vegetable are likely to be good, the salad and glass of wine are likely to be forgotten, the main dishes risky and the desserts one worse than the other.

If that is not yet what one might hope from the new Jour et Nuit, at least one now has a fighting chance.