Rosaryville Road, Upper Marlboro, Md. 20772. 301-856-1860. Open for lunch Tuesday through Saturday, noon to 2:30 p.m.; for dinner Tuesday through Saturday, 6 p.m. to 9:30 p.m., Sunday brunch noon to 3 p.m., Sunday dinner 3 p.m. to 6 p.m. Reservations recommended. AE, V, MC, Choice. No separate smoking area. Prices: at lunch appetizers $3 to $4, entrees $7.50 to $12.50. Fixed-price lunch $14.50. At dinner appetizers $4.50 to $6, entrees $16 to $22. Fixed-price dinners $34. Fixed-price brunch $14.50. Full dinner with wine, tax and tip about $40 to $50 a person.

THE PRINCE GEORGE'S COUNTY jokes are about to become extinct. With the opening of Mount Airy Plantation the county now has dining fine enough to compete with downtown, uptown, any town.

The Calvert family once owned Maryland as well as the Mount Airy Plantation, built in 1725. Now the state of Maryland owns the plantation, but has leased it to the Kulla family, who have restored it as a restaurant and two-suite inn. And they have aimed high.

Once you arrive your car will be parked, you will be invited to take your drinks before the fireplace in the lounge, or perhaps you will be offered a tour of the estate. You can have lunch or dinner in a small dining room or in a large glassed-in atrium with french doors leading to the terrace-to-be.

This is an ambitious restaurant. The hurricane lamps on the tables hold real candles, the rolls are homemade, and the service is well rehearsed -- a little self-conscious, but thorough.

Occasionally the dining room has been left unattended, which is a common problem in restaurants with multiple dining rooms; I wish more restaurateurs would understand that some staff should always be in view, lest a dinner grow cold while a fork is needed.

The food shows more sureness, though the kitchen has been slow even when the dining room was less than half full. And the menu follows the seasons. In winter there was quail pa te', mild and smooth, studded with ham. And there were oysters with a vinegar-shallot dipping sauce rather than the standard red cocktail sauce. Mussels were served out of the shell and napped with a lovely mellow white wine cream sauce. Among the heavier appetizers there were puff pastry barquettes filled with a thick onion cream, too floury and too mild, but rescued by superlatively light pastry. And lamb ravioli were too thick a pasta, but intriguing thanks to a highly seasoned ground lamb filling and glossy dark brown minted sauce. A duck broth with pheasant dumplings was an intense melding of flavors, and its spicy dumplings had the lightness I missed in the ravioli.

Summer appetizers are lighter: ceviche, cold pea soup, a "spring terrine" and clams, removed from their shell and tossed with a light briny thyme cream. They were delicious, the clams warmed rather than cooked, the thyme aromatic and fresh. Another surprising appetizer was strips of saute'ed chicken breast in a small ramekin, moistened by a very tart lemony cream sauce with julienned peel and tiny mushrooms.

While the menu is not large -- maybe a dozen main dishes -- the choice is difficult because each has a compelling twist. Steak comes with blue cheese and shallots or the tomato-spiked variation of bearnaise known as sauce choron. Whichever way it is done, the trout is a good choice here. No tasteless anonymous fish fillet, this is firmly fresh with a definite trout flavor, and it is grilled so the skin is crisp and the flesh soft and juicy. Rainbow trout might be stuffed with a salmon mousse or topped with a saffron cream or saffron and sweet peppers. Another advantage of ordering fish at Mount Airy is that this chef whips up butter sauces that are very light in texture but full in flavor.

He also prepares a beautifully cooked and aromatic rack of lamb infused with fresh herbs, though better trimming would cut its greasiness. Steaks and chops here show art in the buying and in the grilling. Other meats, though, displayed awkwardness. Veal scallops were overpounded and cooked excessively on one side so they were both hard and mushy, a difficult combination of mistakes. And pork with apricots tasted only of apricots, little of pork.

With these main dishes come bright fresh vegetables, and red-skinned potatoes that serve to absorb the last of the sauces.

In all, it is fairly light food, in modest portions that leave room for dessert -- and great store is set by Mount Airy's desserts. The chef makes clever ice creams and sorbets -- grapefruit cinnamon sorbet, perhaps, or rum walnut ice cream. There are prettily layered molds of ice creams and sherbets. And there is an astonishing array of tortes and tarts -- multilayer chocolate ganache cake, hazelnut raspberry cheesecake, white chocolate pecan tart, apple cranberry pie, macadamia coconut tart, chocolate chestnut cream tart. Even the most inglorious of them is pretty good, and the tarts in particular can be sensational. You can finish with a choice of coffees and teas, and are more than likely to be invited to tour more of the house.

There is still much to be done at Mount Airy. The wine list is not yet a source of pride, but the Cruvinet system allows you to sample some good wines by the glass. The garden needs work, and there is an unfinished air to the place that is not to be blamed only on the dirt entrance road.

The other way to look at that is that Mount Airy allows a sense of discovery. And I doubt that the road will keep the county -- and the metropolitan area -- from beating a path to this gracious door.