MARROCCO'S 1120 20th St. NW. 331-9664 Open for lunch Monday through Friday 11:30 a.m. to 3 p.m., dinner Monday through Thursday 5 to 10 p.m., Friday and Saturday 5 to 11 p.m. Closed Sunday. No separate smoking section. All major credit cards accepted except Choice. Prices: Most dinner appetizers $4 to $5, entrees $7 to $12. Complete dinner with wine, tax and tip about [TEXT OMITTED FROM SOURCE]

DOCTORS, GARDENERS AND restaurateurs will agree on one thing: Transplants can be tricky. In the case of restaurants, a move to a new location can mean a loss of old virtues or the acquisition of new vices. But sometimes a restaurant can flourish in a new environment.

Take Marrocco's. Until a couple of years ago it was an old-fashioned, moderately priced Italian restaurant on Pennsylvania Avenue. Then it moved to a spiffy office-building complex nearby. How did it adapt to this rich new soil? For one thing, the ambiance took a great leap forward. The new Marrocco's is smooth, suave, soft-edged, gracefully appointed, eminently comfortable. The colors and lighting are muted, the acoustics good, the tables nicely spaced. (The best seats in the house are in the bay windows overlooking the street.) To the management's credit (and good sense), the prices didn't share in the great leap. So the move has resulted in a happy combination: a handsome dining environment, plus moderate cost.

The menu is largely standard Italian: hot and cold appetizers; pastas in the usual assortment; veal, chicken breast and shellfish topped with tomato or cream-based sauces; fresh fish, and individual-size pizzas. The food has its ups and downs, but there are enough of the ups so that you can dine quite nicely here if you order carefully. Raw materials, from the salad greens to the veal, are generally top-notch. Marrocco's main weakness is a tendency toward excess: Some dishes are swamped with too much cheese or too much sauce, or both. And some of those sauces are flat and uninteresting.

The wine list matches the food: mostly standard selections at very attractive prices. There are the usual Italian whites, with a decent Cavit pinot grigio at only $8.50, a better corvo at $10.50. Among the reds, look for the 1980 Mondavi pinot noir, deep colored, full bodied, nicely astringent, and the 1981 Mastroberardino taurasi, smooth, silky, clean-tasting.

The bread at Marrocco's deserves special mention: It's the authentic Italian article, hearth-baked, thick-crusted, fresh and increasingly rare in restaurants these days. If you start your dinner with the outstanding mussels, you can use the bread to sop up the heavenly tomato-wine-garlic-olive oil broth. The fried appetizers are impressive, too: The calamari are tender and lightly battered, and the mozzarella in carrozza is creamy, free of excess oil and not overanchovied. Carpaccio is first rate, the raw beef razor-thin and delicately flavored, the accompanying mustard sauce properly zingy. Cold marinated asparagus, when it's available, is outstanding. But steer clear of the clams with garlic and oregano, hopelessly buried in bread-crumb mush. Except for an unfortunate tendency to overdress them (the problem of excess, recall), salads are nicely done here. So are the soups, particularly the rich, homey pasta e fagioli. The individual-size pizzas are pleasant enough, with nicely chewy crusts and plenty of garlic. The seafood and vegetable versions are particularly noteworthy, their toppings carefully kept from drying out.

Pastas, made on the premises, are cooked to the proper tender-chewy consistency, but not all the sauces do the pasta justice. The secret to getting a good one? Sidestep anything that says "cream" or "cheese." Fettuccine carbonara, for example, is glopped with so much creamy, cheesy sauce that it glues the pasta into a sticky mass. The alfredo version is equally overrich and suffers from terminal blandness. Cannelloni could be wonderful; the pasta crepes are exceptionally delicate, with lightly browned, nearly crisp bottom surfaces reminiscent of good blini, and with excellent ground veal-spinach fillings. But the delicacy is all but smothered under a thick shroud of cheese and an overabundance of sauce. The same problem afflicts the otherwise excellent manicotti. Pasta winners? The tenderest of baby clams in a simple oil-garlic-parsley sauce, and a lively spaghetti bolognese with meaty, delightfully fruity tomato sauce (at $5.95 a nice buy).

Among the entrees, the osso buco is top-notch, a flavorful piece of veal shank properly cooked so it's falling off the bone, and served in a robust (if a bit overoily) tomato-based sauce with diced onion and parsley. (For a special treat, don't forget to scoop the rich marrow out of the bone.) Veal is a first-class product here, fine-textured and unusually flavorful. To best appreciate the flavor, try it saute'ed in a bit of egg batter with lemon (vitello francese); or, for something zippier, in a gutsy, chunky, nicely peppery tomato sauce with capers (veal pizzaiola). As with the pastas, avoid the veal dishes with cheese (saltimbocca, for example), which have so much of it you won't taste the meat. There are half a dozen or so chicken breast dishes, all pleasant, none remarkable.

The broiled fish has been reliably fresh, cooked carefully so that it's firm and moist, and served simply with lemon-butter-herb sauces. But we've found the shrimp a bit iffy -- sweet and fresh-tasting on one occasion, a little off on another. The best shrimp bet is scampi caprese, with a good fruity, garlicky tomato sauce. There are decent scallops, too, with diced fresh tomato, but they come with a basically bland sauce that's overdosed with dried herbs.

For dessert there are pastries, made elsewhere, and an acceptable if oversweet cannoli. The most refreshing finish is the odd-but-good tortoni, rum-flavored and with the consistency of soft ice cream.

Marrocco's is not a memorable restaurant, nor is it a place where you can choose anything on the menu and be pleased. But if you select wisely you can design a very good meal here, enjoy it in a lovely dining room, be well served by a considerate and professional staff and not flinch when it's time for the check. The transplant has taken. -- Mark and Gail Barnett MARK AND GAIL BARNETT are free-lance restaurant critics and regular contributors to this column.