The menu demurely says "southern-style food," but what the Florida Avenue Grill serves up -- in robust portions, at wonderfully old-fashioned prices, and in a no-nonsense, lunch- counter-with-booths environment -- is soul food. Although it's been in business since 1940, this is no venerable Washington institution sliding by on its reputation. The food is still tops, and, judging by the crowds of serious eaters, the customers are still loyal. Some of the dishes are merely good, like the hefty meat loaf and the pork chops, both with brown gravy. Or the meaty barbecued ribs, with a sweet glaze. But some are marvelous. The corn bread, for example, hot out of the oven. And the fried chicken, which just might be the best in town. Or the baked chicken with cornbread dressing. Or the collard greens. Or the black-eyed peas, with the essential cube of pork fat oozing flavor into the bowl. There's a pitcher of ice water on each table (an idea they haven't thought of yet on K Street). Or you can wash down your fried chicken with good, strong iced tea, but be warned that it's made southern style, with enough sugar to curl your toes. For dessert, the chocolate cake will remind you of a Tastykake cupcake, but the peach cobbler is just right. 1100 Florida Ave. NW. 265- 1586. L, D $3.10-$6.35. Closed Sun. No credit cards. No liquor.