A FEW YEARS AGO, TAPAS fever was reported around the country, but the trend left Washington cold. Tapas, those little plates of appetizers that Spaniards nibble with sherry to tide themselves over until their late dinners, have long been available in Spanish restaurants here, but they have been little noticed. Now, after we long ago gave up looking, a trend seems imminent. Here's a look at four restaurants -- two American and two Spanish -- that are on the cutting edge.

TWENTY-ONE FEDERAL -- 1736 L St. NW. 331-9771. Tapas served weekdays 5:30 to 7:30 p.m. All major credit cards. Prices: $3.50 each.

THE GOOD NEWS IS THAT THE TAPAS are a sampler of Twenty-One Federal's wonderful appetizers at only $3.50 each rather than the usual $7 to $9. The bad news is that they are served only weekdays between 5:30 and 7:30 p.m. and only in the lounge.

Still, Twenty-One Federal's tapas present a bargain-priced opportunity to sample this glorious restaurant's cooking. The tapas menu has 20 items, though only half a dozen are available on any day. My favorites are the raw things: the vivid Southwestern steak tartare with its two sauces, and the swordfish carpaccio, which looks like a veil of fish sprinkled with olive oil, fennel, pine nuts and raisins. Beans are a theme here: black beans with light, spicy corn cakes; white beans with sausage or on the excellent bruschetta. There are delightful little meat dishes: Peking duck rolls, lamb brochette, beef satays, meatballs with spicy chorizo. Potatoes are dazzling with smoked salmon or in a warm salad with crayfish, artichokes and andouille sausage. And the ethnic range stretches from Japanese chicken yakitori to Italian grilled squid with polenta. Portions are the size of normal appetizers, which makes it easy to share tastes around the table.

If you're looking for an exotic drink, Twenty-One Federal makes a rum punch that tastes about 300 proof; but the planter's punch, a gorgeous tricolored drink with three kinds of citrus wedges, is far more refreshing. SUZANNE'S -- 1735 Connecticut Ave. NW. 483-4633. Tapas served weekdays 4:30 to 7 p.m. MC. Prices: 25 cents to $1.50. THE NARROW LEDGE BEHIND SU- zanne's bar is filled with bowls and plates at cocktail hour on weekdays from 4:30 to 7 p.m. I found a dozen choices when I visited, and while the prices are not posted, they are far from alarming. Stuffed grape leaves, sausage in puff pastry or cheeses are less than $1, a potato omelet is $1, empanadas and samosas cost $1.25 each. A waitress will serve you, or you can help yourself.

Surely there's a catch, you figure. And there is. The food doesn't taste half as good as it sounds -- or looks. The best part is the free tapenade, a mild version of France's black olive/anchovy paste, gray here instead of black and not nearly as strong or salty as is usual. House- made breadsticks are available for dipping. Grape leaves are pasty and too tart, squid with soba noodles gummy and oversalted, the potato omelet flavorless, and the pastry-wrapped tapas -- samosas and empanadas -- admirable dough with dry and dull fillings. Chorizo in puff pastry needs zip -- mustard would help -- and shrimp on sugar cane, though tasting wonderfully of shrimp, is gummy. The most filling appetizers are better values: skewers of potato, egg, artichoke hearts and pickled onions with fresh dill; and tuna-stuffed French bread wedges. The jerk pork is hardly Jamaican and slightly chewy, but it is a zesty, spiced skewered pork.

Suzanne's bar choices shine, with three kinds of sherry and an impressive selection of beer and wine by the glass. It is a relaxed and friendly place to spend a late afternoon, particularly when you are tired of engaging your critical faculties and just want to unwind and nibble in peace. EL BODEGON -- 1637 R St. NW. 667-1710. Tapas served at lunch Monday through Friday 11:30 a.m. to 2:30 p.m., at dinner Monday through Thursday 5:30 to 10:30 p.m., Friday and Saturday 5:30 to 11 p.m. Closed Sunday. AE, MC, V. Prices: $3 to $6.95. EL BODEGON FEELS LIKE SPAIN, SMELLS like Spain, tastes like Spain. Just inside the entrance is a small barroom with a long, very Spanish tapas list. Overhead, whole hams hang interspersed with ropes of red peppers and garlic. The waiters are jovial and friendly. And sometimes late in the evening the maitre d' wanders around pouring wine into diners' open mouths; sometimes a guitarist plays.

The tapas number nearly two dozen and cost from $3 to $6.95. Served in rustic pottery casseroles, they are hefty portions; three per person could easily serve as dinner. Sauces are knockouts, some spiked with red pepper, some oily and some tomatoey, many thick with minced garlic and all worthy of sopping up with bread. So concentrate on those dishes with sauce: plump stuffed squid flavored with ham, garlic and parsley in a sauce of squid ink and red wine. Scallops and mushrooms swim in an irresistible, tart, spicy butter sauce. Snails or mussels are good excuses for more garlicky herbed sauces. I am less enchanted with El Bodegon's fried tapas. And while the salty, smoky ham is commendable, in previous years it was better. The chorizo is dreary. Among cold dishes, potatoes in garlic sauce is thrilling if you're looking for a way to keep away werewolves.

El Bodegon has a better selection of tapas than of sherries, so you'd be better off sharing a bottle of modestly priced Spanish red wine or a pitcher of sangria. TABERNA DEL ALABARDERO --

1776 I St. NW. 429-2200. Tapas served Monday through Friday 11:30 a.m. to 10:30 p.m., Saturday 6 to 11 p.m. Closed Sunday. All major credit cards. Prices: $1.50 at the bar, $1.75 in the restaurant. THE TAPAS BAR OF TABERNA DEL Alabardero has only three tables and some bar stools plus a display of open-face sandwiches and cold dishes. But it serves tapas all day and offers a couple of treasures. One is the sherry variation, manzanilla, dipped from a barrel into a small, narrow sherry glass. Another is the tortilla -- cold potato omelet -- easily the best in town, even when it is too salty. And the paper-thin ham is outstanding. Marinated octopus has rare finesse -- silky rather than rubbery, marinated with peppers and onions in fine olive oil. Snowy white marinated smelts are pleasant, as are the mild, fat green olives. Disappointing have been the flabby and salty open-face sandwiches, the oily and bland chorizo and greasy fried squid, for which we were charged $7.90. Don't plan to hurry at Taberna; communication is erratic, and service is intermittent. So just sit back and watch the passing scene.