LA POSADA; 8117 Woodmont Ave., Bethesda. 656-9588. Hours: Open: for lunch Monday through Friday 11:30 a.m. to 2:30 p.m.; for dinner Sunday through Thursday, 5 p.m. to 10 p.m., Friday and Saturday 5 p.m. to 11 p.m. All major credit cards. Reservations suggested. No separate smoking area. Prices: appetizers $3.45 to $4.95, entrees $5.75 to $11.95. Full dinner with drinks, tax and tip less than $20 a person. EL CARIBE; 8130 Wisconsin Ave., Bethesda. 456-0888. Hours: Open for lunch Monday through Friday, 11:30 a.m. to 5 p.m., Saturday and Sunday, noon to 4 p.m.; for dinner Monday through Thursday 5 p.m. to 10:30 p.m., Friday and Saturday 4 p.m. to 11:30 p.m., Sunday 5 p.m. to 10 p.m. All major credit cards. Reservations suggested. No separate smoking area. Prices: at lunch appetizers $2.95-$4.50, entrees $6.50 to $12.50; at dinner appetizers $3.25 to $4.75, entrees $8.50 to $15.95. Full dinner with wine or drinks, tax and tip $25 to $30 a person.

EVERYONE, IT SEEMS, is looking for a good Mexican restaurant. The man at the bicycle shop asked me if I knew one in Silver Spring, then proceeded to tell me about La Posada, which he had discovered because an advertisement made it sound authentic. Then a friend told me about La Posada, which her husband also found through an ad. And how did I find La Posada? (Better yet, what prompted me to search for a half hour back and forth along Woodmont Avenue?) Also through an ad. The lesson is not simply that it pays to advertise, but that Washington is still short of good Mexican restaurants.

As it turns out, La Posada is not the Mexican restaurant of our dreams. But it is a cut above most in its cooking, and its dining rooms -- a small cozy room decorated with tiles and handwoven fabrics, plus a seven-table rooftop open-air space with indoor-outdoor carpet -- are more charming than most.

The menu starts with the familiar: nachos, quesadillas, enchiladas, burritos, fajitas, chimichangas and combination plates. But it goes on to red- and green-chile stews, seafoods, egg dishes and even hamburgers. While a few dishes climb above $10, you could easily eat at La Posada for under $10 -- a rare treat in a Bethesda restaurant with some charm.

Your first hint that La Posada could be exceptional comes immediately: The warm tortilla chips are thinner and more flavorful, as well as less greasy, than the usual Tex-Mex chips. The salsa is crunchy and lively with onion and bits of fresh tomato; it varies from mild to hot depending on the day, but it has enough taste that it would take only a bit of hot sauce to make it suitable for the bravest chili-head.

This is a menu that warrants careful picking and choosing. The chiles rellenos were thickly spongy and heavy, the guacamole in need of seasoning. And shrimp wrapped in bacon -- Camarones Mazatlan on the menu -- were good ingredients but a misguided fancy of cheese, corn, cocktail sauce, pineapple and maraschino cherries. The chef must have been hanging around the Luau Hut.

But there are those endearing touches that make you forgive La Posada. The quesadillas -- which can be ordered with bacon and mushrooms or marinated steak along with the jack and cheddar cheese, scallions and green chiles -- are admirably thin flour tortillas, well stuffed and topped with a pretty rosette of sour cream piped on top. Salads are large and garnished with flair. Fajitas are generous in their sizzling strips of meat, well sparked with onions, green peppers and the vinegared marinade. Huevos rancheros are made with properly runny eggs that blend into the pungent ranchera sauce. And the chile verde -- pork chunks in a green chile sauce -- is a wonderful stew that demonstrates the flavor as well as the heat of green chiles.

The accompaniments also show care; though the red rice is indifferent, the refried beans are creamy and spicy, insulated with a layer of melted cheese. In all, the food is rich with profuse gratings of cheese that melt over nearly everything. It is gutsy peasant food, served in large portions, and likable and interesting even when it falls short of excellence.

The unforgivable exception is one dessert that makes even the shrimp with maraschino cherries look good: The menu lists it as deep-fried ice cream -- an idea that is hard to resist. The reality is third-rate ice cream rolled in crumbs that taste like stale soggy cornflakes, and greasy as well. If you want ice cream, you'd better stay north of the border.

There is a kicker to this, which an avid menu reader might spot. Just around the block is the newest branch of El Caribe. Its Latin American menu is long and varied, ranging from Spanish paella and stuffed squid to Argentina's churrasco and Bolivia's beef tongue. An entire page of the menu is Mexican dishes, the familiar enchiladas, fajitas, burritos and tacos. And at the bottom is shrimp wrapped in bacon with corn, cocktail sauce and pineapple. Aha, the genesis of La Posada becomes clear. It is a Mexican outpost of El Caribe -- they have the same owner and in fact share a kitchen. No wonder it stands above the ordinary.

As it turns out, El Caribe's fajitas are identically generous and savory, its refried beans every bit as deliciously unctuous. And its non-Mexican dishes are generally terrific, at least the more earthy ones.

Don't opt for the luxuries. I found the zarzuela a pretty dull casserole of overcooked seafood in a highly brandied broth. In fact, I found the seafood generally overcooked, though the appetizer gambas al ajillo escaped that fate, and was a delectable dish of butter sauce with mellowed garlic slices, worth ordering just for dipping up the sauce with bread.

El Caribe serves superb empanadas, their filling sharp with olives, sweet with raisins, hearty with meat and gentled with chopped eggs. They are the best empanadas I've found since Sam's Argentine Bakery left Georgetown. And a meal at El Caribe ends on a higher plane than La Posada, particularly with the homey sponge cake roll filled with nutted cream and known as brazo gitano.

Both restaurants offer service that is brisk as well as friendly. El Caribe's is more polished, but then so are its surroundings -- the dark wood and white walls, the ceiling fans lulling you into a lazy rhythm.

If your tastes are broad, your purse is a little more generous and your style is more elegant, El Caribe would be your attraction. If you seek strictly Mexican food and are satisfied with rustic coziness, you'll be more interested in La Posada; the prices are similar for any one dish, but La Posada emphasizes less expensive foods, while El Caribe offers more ambitious cooking. They both add to the evidence that Bethesda is becoming an awfully good restaurant town.