Open Monday through Thursday 11:30 a.m. to 10:30 p.m., Friday and Saturday 11:30 a.m. to 11:30 p.m. Reservations. AE, MC, V. Prices: At lunch, main course with soup and tea, $3.50 to $6. At dinner appetizers $1 to $4, main dishes $4.25 to $15, average $6 to $12.

While innumerable new Szechuan and Hunan restaurants, from Rockville to Fairfax, lock chopsticks, somebody has come up with what sounds like a better idea: a Chinese seafood restaurant.

And if you could judge a restaurant by its menu, China Harbor would soar above the Oriental competition, in its breadth, its unique choices and its fair prices.

But you can't eat the menu, and this one leaves too many promises unfulfilled.

What could be more promising than a tank with live trout, its supply actually depleting throughout the evening, so you know those lively fish are not just for show. And its neighbor is a lobster tank, your choice brought to wiggle at you before it is turned into dinner. On the tables are cards announcing soft-shell crabs ($10 weekdays, $12 weekends) with black bean sauce, ginger and spring onions or brown sauce. The lobsters and trout, also $12, can be similarly sauced, or the lobster served braised or Cantonese-style.

Beyond the live offerings are 15 shrimp dishes, from moo shi shrimp to "jumbo shrimp double delight." Sea bass, flounder or yellow fish can be steamed whole; hard-shell crabs are prepared seven ways. And then there are snails, squid, abalone, sea cucumbers, scallops, oysters and clams, as well as a page of meats and a page of noodles and vegetable dishes. This is no run-of-the-mill regional Chinese menu.

But these fish swim in troubled waters in making their way from tank to table. A look at the back of the dining room one Friday evening would have been enough to suggest slipshod management: A mess of dishes and tablecloths piled up around the kitchen entrance. Other signs of indifference showed later on the plate.

In the several seafood soups there have been lovely, supple bits of fish or seafood, but they floated in broths with little more flavor than the Atlantic Ocean. And a shrimp ball soup sank into the depths with its crumbly, grainy shrimp balls.

Sometimes I think there is an inverse relationship between the dumplings and the rest of a Chinese restaurant. At China Harbor, for instance, the dumplings were excellent, their dough thick and chewy and more like dumplings than like noodles, their filling juicy and spicy with shrimp as well as meat. They were the only appetizer we tried that was better than routine. Smoked fish was gnarled and soggy; fried oysters were greasy, doughy and overcooked; marinated cabbage tasted like nothing more than raw cabbage doused in vinegar; and baked clams were fine but no more than what the waiter called them as he plunked them on our table: clams casino--just clams baked with a square of bacon.

Among main dishes, steamed flounder was being served at table after table. And no wonder; it looked beautiful, the enormous whole fish topped with bits of julienned pork and aromatic vegetables. But the flounder was gelatinous, its flesh beautifully white but damp, its sauce soupy. And the trout from the tank was handsomely curved upright on the platter, but it was overcooked and rubbery, its brown sauce spoiled by sour-tasting black mushrooms. Another day a feisty-looking lobster was overcooked and lost in a overly sweet, tomatoey braising sauce. Crabs have been mushy, whether hard-shell or soft-shell, though one can hardly go wrong by stir-frying crabs with ginger and spring onions or with black beans, onions and green peppers. Oysters done with ginger and spring onions, though, can go very wrong if the oysters are not fresh from the shell and if they are cooked until chewy; these oysters tasted as if they suffered both such insults. In fact, the best of the main dishes I tasted was a noodle dish, "san-sen ja-jun mein," which was a bowl of egg noodles and bowl of dark sauce with bits of meat and what seemed to be sea cucumbers (even the waiter wasn't sure) to mix together at the table into one mellow and slithery combination. And if you like to linger over dinner, the baby snails, to be painstakingly extracted from their shells with toothpicks, are fun and pleasantly flavored with black beans or ginger and spring onions.

Still, the restaurant's outstanding effort in presenting a wide variety of seafoods and several fresh from the tank is lost on these preparations, which are not nearly as good as the fish at many less-specialized Chinese restaurants.

Service is harried but efficient, and damp cloths presented after the meal are appreciated after crab in the shell and the like. The environment is similarly harried, with pictures on the wall either lighted or three-dimensional or sculpted from jade-colored stone, and plants hanging all around. On a crowded evening, the heavy oil smell from the doughnut shop next door can be oppressive, and the room is noisy. Icy Tsing Tao beer helps, but don't look to the wine list for much solace.

In all, China Harbor is an outstanding idea reduced in its execution to the ordinary.