1052 Rockville Pike, Rockville 251-9808 1835 University Blvd. Langley Park (opening soon) 8239 Georgia Ave., Silver Spring (opening soon) Hours: 11 a.m. to 9 p.m. daily. Prices: Chicken platters $2.85 to $4.89. Cards: None accepted.

First there was one El Pollo Primo in Rockville. Then another on Columbia Road in Washington. Now two more, one in Langley Park, another in Silver Spring, are set to open around the first of the year.

There's good reason for all this growth. El Pollo Primo offers fast food for eating in or taking out that's extraordinarily good, remarkably cheap and a lot less fatty than the usual burgers or fried chicken.

The mainstay of the menu is Mexican broiled chicken, marinated in a mixture of citrus juices, herbs and garlic, then cooked on an open grill. To help whet your appetite, you can watch the grilling as you enter -- fancy restaurants aren't the only ones with open kitchens.

This chicken is terrific: moist and tender all the way through, infused with the flavor and fragrance of the garlic and herbs, and with a delicate, semicrisp skin.

The birds are big, so that even the two-piece platter at $2.85 (which comes with a choice of two side dishes) is a good-sized meal. That's a noteworthy bargain. And note too that if you're taking food home, you can get a whole chicken for $6.99; with a few ancillary items from the refrigerator, it will feed four people very nicely.

The chicken comes with tortillas and salsa, a mild version with chopped tomato and cilantro or a hotter one made with green chili peppers. Strip the meat off the bones, add some choice pieces of skin, slather on a bit of salsa, roll the whole thing up and you've got a scaled-down version of Peking duck. Unfortunately, the tortillas here can be pretty leathery, so we prefer the chicken as is.

Most of the side dishes are unusually well prepared. The rice, cooked in a giant stainless steel drum, is remarkably firm for all the sitting it has to do, and it's nicely flavored with tomato, peas and bits of onion. The beans are excellent, too, firm kidney beans cooked with chili pepper. They are a good companion for the rice -- try mixing the two and blending in salsa to taste.

The coleslaw is top-notch, fresh, bright, crunchy -- not watery or over-sweet.

The corn on the cob? Mushy and waterlogged. What can you expect from steamed corn in winter?

There's a new wrinkle at El Pollo Primo: chicken salad. It's a chunky gem of a chicken salad, too, with big tender pieces of chicken, chopped celery, green pepper, black olives, a hint of onion flavor and, blessedly, not an excess of mayonnaise. It comes ringed with tomato quarters in a big, fluted, fried flour tortilla that's lined with lettuce.

The idea is to break off bits of the fried tortilla to eat with the salad. Not a bad plan, except that the cold tortilla tends to be unpleasantly damp -- perhaps they ought to work on a way to crisp it right before serving. At $2.89 for an adequate but not huge portion, the chicken salad isn't overpriced, but it's not nearly so big a bargain as the broiled chicken.