Open for lunch Monday through Friday, 11:30 a.m. to 2:30 p.m.; and for dinner seven days a week, 5:30 to 11 p.m. AE, C, MC, V. Reservations. Prices: Full dinner $15 to $20 a person, including wine, tax and tip. Main courses $5.75 to $10.95.

Capitol Hill is on its way to becoming self-sufficient, at least in culinary terms. The latest step along the path, which is now paved with American, French, Italian, Greek, Swiss, Mexican, Irish and Arabic restaurants, is a new Spanish restaurant, Los Asturianos, the third major restaurant to open on Barracks Row in the past year or so. While Los Asturianos might struggle if it were in the competition with Spanish restaurants downtown and in Georgetown, its cuisine is a welcome change on Capitol Hill, enough to fill the tables on Friday night.

Los Asturianos is an appealing restaurant in many ways that I will take pleasure in elaborating. But it has had one major problem that pervaded my visits: its seafood, which dominates the menu, lacked freshness. The flavors of the mussels and fish filets, which appeared in dish after dish, were strong and bitter. The lobster, which was the star performer in a mixed seafood grill, had a crumbly, mushy texture. Shrimp were iodiny and rubbery. Only squid and scallops were sweet and tender.

It is a pity, because otherwise Los Asturianos is a good restaurant. On the other hand, the problem is easily solved and may even have been overcome by the time this reaches print, since in most other ways the restaurant is succeeding in its earnest attempts to please.

From the outset, the awnings over the windows of this third-floor restaurant pique interest. The dining room, up two short flights of stairs, is surrounded by windows on three sides. A skylight lets in even more light. It is a pretty perch. The dining room is carpeted in quiet red geometry, the waxed blond wood tables left bare to match the modern wood chairs. Tables are well spaced. The walls are warm rough fabrics. And a major part of the room is taken up with a bar lined with bottles of Spanish wine and framed in rustic dark wood. The effect is contemporary and comfortable, though not specifically Spanish. Waiters, however, are dressed in typical Spanish black pants and vests, and serve with the flair of flamenco dancers. On one visit the service was astoundingly slow, but I presume that was an aberration, since other tables were served with dispatch, and I found well paced service thereafter.

A promising start for dinner is sangria, delivered in a large glass pitcher with, typically, a wooden spoon left in it. The drink is mildly tart, far more refreshing than the soda-sweet wine drinks that often pass for sangria. And it mates well with appetizers.

Spain is known for its tapas, or appetizers, and Los Asturianos likewise shows to best advantage in its beginnings ($1.95 to $3.95). Mussels in vinegar sauce are served cold in a creamy vinaigrette chunky with diced sweet red peppers and onions, the combination pungent but not overpowering the mussels. Fried squid are an equally rewarding choice, dipped in a light batter as crisp and airy as tempura. Shrimp in garlic butter are worth trying, and you might as well plunge right away into the garlic fumes which will envelop your table until dessert. A meal at Los Asturianos is permeated with garlic, enough to protect you for a week from whatever evils garlic is said to prevent. But if decisions are difficult for you, order the entremeses variados ($2.50 at lunch, $4.50 for two at dinner). It presents samples of those piquant mussels as well as chorizo, salami, ham, sardines, eggs, cheese and greens. If you have acquired a taste for tripe, the fragrant callos a la madrilena will satisfy such a craving; its tripe is cooked to a soft, gelatinous state in a terra cotta colored broth savory with the flavors of Spanish sausage.

Here is a restaurant that attends well to its soups ($1.50 to $2.75). The best - and perhaps the best dish on the menu - is fabada Asturiana, a bean soup teasingly spiced with sausage. The gaspacho is a good version, light and creamy pink. And seafood soup is a vivid saffron-gold broth plentiful with shellfish, peas and pimentos (the two secondary themes of Los Asturianos, after garlic); if the seafood were fresher the soup would have been grand. Garlic soup is the least exciting of the soups, and you are not likely to leave dinner feeling a dearth of garlic anyway.

Veal is, surprisingly, the best of main courses I tried. Ternera Riojana ($7.25) is tender slices of pale veal in a translucent sauce spicy with chunks of sausage and strips of pimento. Paella ($7.75) is done well, moist and briny golden rice competing to fill the casserole with chicken and all kinds of seafoods, ham and sausage. Other seafood dishes showed promise; zarzuela floated its seafood in a faintly sweet and very savory, winey sauce. The most expensive dish on the menu, parrillada ($10.95) was an imposing presentation of half a lobster, mounds of shrimp, scallops, fish and mussels grilled with garlic, lemon and butter and served with a garlicky mayonnaise for dipping. Shorter cooking and fresher seafood would have turned it into a stunning dinner. The menu also lists several other seafood dishes - merluza a la vasca being the most typically Spanish, but a bland rendition - a couple of steak preparations and three chickens, including a delicate breast of chicken cut into strips and sauteed, served in a wine sauce similar to the veal ($5.75). It, too, repeats the peas-and-pimento theme. With main dishes came good, chewy rice, fresh cooked carrots - unremarkable - and some particularly worthy, crusty bread.

Dessert is a minor note at Los Asturianos, though the flan is outstanding, rich and eggy and fragile. Otherwise, there are ice creams and fruit desserts the likes of pears cooked to a near jelly in a supersweet wine glaze.

A choice of interesting restaurants is a recent phenomenon on Capitol Hill. Thus, while the opening of Los Asturianos is not vital news to those who have already found a Spanish restaurant elsewhere that they enjoy, it enriches the dining possibilities of its neighborhood.