Open for lunch Monday through Friday 11:30 a.m. to 2:30 p.m., dinner Monday through Thursday 6 p.m. to 10:30 p.m., Friday and SATURDAY 6 P.M. TO 11 P.M. AE,MC,V.Reservations suggested. Prices: At lunch, pastas (appetizer portions) $5, main courses $4 to $10. At dinner, appetizers and appetizer portions of pasta average $4.50 to $6, main disher average $15. Full dinner with wine, tax and tip about $35 a person.

Why do they do it? Restaurateurs repeatedly try to leap tall buildings (and fall to their deaths) when they could, more slowly but far more surely, walk around them. They open a new restaurant and immediately price themselves at the top, not asking themselves why a diner should risk his money on an untried restaurant when sure bets are waiting for his patronage. They expect the customer's wallet to bear the risk, to pay top dollar for an unknown and certainly newborn and shaky product.

Washington's romance with new restaurants is over; the public is no longer flocking to them just because they are new. Thus with Tartufo we have another restaurant that by most standards would be considered good, but charges the public as much as years-older, more stable and well-known restaurants. And thus empty tables are undoubtedly pinching the resources of the restaurant.

Tartufo, as the name and the pasta list suggest, is Italian. It tastes French, however, and even among the daily specials -- in between the risotto and veal chop "Bolonesa" -- are duck liver mousse and salmon with choron sauce, that lovely tomato-tinged bearnaise. The standing menu includes rockfish with fennel and basil, stuffed trout Leghorn style and three familarly Italian veal dishes, as well as six pastas. It also includes grilled Dover sole, frogs' legs provencale, chateaubriand, rack of lamb (with grapes) and duck (with amaretto), the standards of French restaurants in America. The restaurant looks quite American, the first floor of an office building transformed with velvety upholstered chairs, soft carpeting and contemporary globe lamps into a soft, lush setting that retains a residual office-building boxiness. The room is brown and beige, with a pink rose on each table, a color theme repeated right down to the chocolate cake with pink roses on the dessert trolley.

One can concoct a delectable dinner at Tartufo. It could start lightly with smoked salmon, hand-cut to paper thinness and decorated to resemble a fish; or more substantially with large, fat ravioli stuffed with spinach and sauced with a walnut and nutmeg cream. The pastas can be excellent, the filling for the cannelloni as airy as a mousse, the fettucine supple and cooked al dente. The pesto, which has sauced many of the pastas during basil season, is grassy with fresh herbs, made more gentle by the addition of cream. It is good, but emphasizes that the chef's taste is for subtlety rather than pungency. (Sometimes, as with a cream cheese and salmon sauce for tagliolini, the taste stumbles into blandness.)

Risotto is often among the daily specials, at only $4.50 ($7.50 on the standing menu), whereas most Italian restaurants require it to be ordered for two, at around $16. The risotto sometimes has been too heavily sauced with tomato and unfortunately dampt as well, but still the rice is wonderfully chewy and permeated with its seafood or vegetables or whatever is its daily variation.

Among main dishes, the liver Venetian style has been a standout, though it is available only intermittently. The liver was delicate, thinly sliced and cooked rare, topped with a thickish brown suace and onions cooked to melting, all making a superb blend. Salmon, too, has been served very fresh and cooked just right, its choron sauce a bit sweet but deliciously buttery and pungent. The scampi a waiter recommended looked beautiful, the shrimp butterflied and turned inside out before grilling, lined up, pink and pretty, on a bed of bright green spinach (excellent spinach, as it always is here) in a pool of dilled beurre blanc. But the shrimp -- at $15 -- were tough, dry and iodiny, the weak link of the platter. And veal, which should be expected to be excellent at an Italian restaurant, is good, pale veal, but cooked to stiff dryness. Crushing at $15 and up.

Three dishes on the menu are truffled: risotto (no price on the menu), pheasant ($40) and veal scaloppine ($30). I asked the waiter if the truffles were fresh (knowing they were not in season). He answered, "They are not canned," and that the veal with truffles was exceptionally good. Instead, it was chewy, overcooked veal in a salty, starchy translucent sauce, its truffles devoid of taste. I left half uneaten and told the waiter it had no truffle taste of aroma. His reply was that the chef had said he would be getting fresh truffles in about a month, but in the meantime he wouldn't recommend it to anyone else. That didn't help me at the time, and nobody offered to make amends.

Thirty dollars for a promise. That's the problem with Tartufo. It is attractive, has some very good dishes and serves elegantly, with lovely garnishes, outstanding vegetable accompaniments and a cart of compelling pastries. It may be evolving into a fine restaurant. But not without first building up the confidence of its customers that at those prices every dish is going to meet its highest standards. If you want to keep an eye on its progress, do so at lunch, when the prices are more humble (and the service less laggardly).

Truffles, as I said, are not yet in season. Neither is Tartufo.