Open Monday through Friday, 11 a.m. to 3 p.m.; Monday through Saturday, 5 to 11 p.m. Closed Sunday. AC, BA, CB, D, MC. Reservations. Foods: Viva the garlic shrimp, black bean soup and paella. Style: A few half timbers, a few paintings, and too few waiters. Price: Main dishes average $6 at dinner, $5 at lunch.

THIS WEEK'S off-the-wall gastronomic theory is that Spanish cuisine never achieved the heights of French because the tapas - appetizers - were so good that nobody cared too much about the finer points of what was served for dinner. These two-or-three-bite servings- usually seafood, meat, olives, cheese, even miniature birds - stand with Chinese dim sum, Japanese sushi, and the Swedish smorgasbord as the world's great palate teasers. And one could deliciously travel from Madrid to Malaga, eating in nothing but tapa bars, having garlicky baby eels here, boiled crayfish there, washing it down with sherry, never needing to venture into a full-course meal.

If there is one classic, archetypal, all-pervasive tapa, it is gambas al ajillo, shrimp in garlic, the title of which hardly does it justice. To understand the irresistible tapas, try gambas al ajillo at Don Liborio. The shrimp are fried in a light batter that soaks up their lemony butter, the whole thing overlaid with parsley and as much chopped garlic as most people use in a week. Don Liborio's tapas also include finely ground and strongly spiced chicken croquettes, shrimp in a hot creole sauce that fades before the garlicky version, mushrooms sauteed in garlic butter, and a couple of specialties that the waiter revealed were canned - squid in its own ink, and pickled mussels. Except for the garlic shrimp, they were hardly enough to waylay you long in the appetizers.

Soups, on the other hand, could trap you into making a meal of them. The black bean is light and elegant, its smoky fragrance and crunchy, buttery croutons strong incentive to fill up on the bowlful. Shrimp soup is heavier, even more spicy, a powerfully shrimp flavored rose-beige bisque.

Main dishes at Don Liborio being portions for bullfighters, you could well skip appetizers - if life weren't so short. Another reason for starting with appetizers is to keep you busy while you wait for the paella, which takes thirty minutes. While this rice-chicken-seafood casserole is a Spanish cliche, Don Liborio's version shows why it has been such a mainstay. This saffron-golden mound of rice tastes of the sea, and is thickly studded with mussels, clams, crabs, chicken and ham, enough to populate each bite and keep you going longer than may be prudent; the serving is formidable. Just as imposing - with neither the rice nor the meats - is mariscada, a blend of shellfish and fish swimming in a garlic sea with islands of cheese-toasted bread rounds.

There you have it, the best of Don Liborio, the dishes worth seeking. I could go on about the chicken in a thick brown garlic sauce, polka-dotted with chopped garlic, or a nicely cooked steak a la cubana with scallions and garlic, or even the lechon asado, thinly sliced roast pork served with raw onions. Otherwise, the menu misses a lot of the classic Spansih dishes in favor of more pedstrian broiled steaks and lamb chops, liver or filets of fish. And there are some solid disappointments such as dry, bland masitas de puerco.But the subsidiary touches - fried green or ripe plantains, yucca, black beans and the thick, creamy, mayonnaise-like salad dressing which outshines its greens - are authentic and rewarding. The wines, a mix of Spanish, Italian and French, none over $8, offer a serviceable selection, along with Spanish hard cider and sangria. Fortunately, all this leaves little zest for dessert, because the flan is flabby, and aside from guava shells the other choices are neither Spanish nor exciting. End, instead, with espresso - their version of American coffee is pallid - and another round of the classical guitar that plays in the evenings.

Main dishes at Don Liborio averaged $6 at dinner, $5 at lunch. Those extraordinary shrimps are $2.50 to $3 as an appetizer. At lunch there are a few sandwiches at that same price. If you hit a lucky lunchtime, the $6.75 paella might be on special for $4.50. Sounds worthy, doesn't it, given the red tablecloths and half-timbered attempt at style, along with the evening guitar"

Not so fast. You still have to contend with the service. With the maitre d'hotel who, when you ask for a table for two, throws up his hands and walks off. With the waiter who turns on his heel if you hesitate over your order. With the waiters dashing to and fro to deliver lukewarm food. With the frustration that drove one diner to drip with venom as she asked the waiter to please refill her water glass "if it is not too much trouble." With the annoyance of ordering fried plantains, and the waiter not warning you that your platter already includes fried plantains. If you need a strong stomach for Don Liborio, it is not a matter of the food, but the abruptness of the service. But if you can handle a little mishandling, and garlic is one of your favorite perfumes, put Don Liborio on your list.