Leave all fads at the door. Crisfield's never changes -- except for its prices and its pecan pie, added to the menu this year. Otherwise it is still the same classic-luncheonette decor and simple Chesapeake seafood menu. Depending on the season, the regulars start with oysters or clams on the half-shell -- there are no better around. I'd skip the clam chowder, which is thick without being creamy. And I'd go on to the fish of the day, preferably flounder or bass, stuffed with crab, undoubtedly the benchmark for imperial crab stuffings. Perfect fish, suave and wonderful lightly bound crab, a mound of crisp homey shoestring potatoes and sweet but creamy-crunchy coleslaw make the fish dinner to dream of. In season I'd also go for the soft- shell crabs; and if nobody from Maine is around to complain that they are cherrystones rather than steamers, the fried clams are beyond reproach. Then there are the buttery pan-cooked Norfolk dishes, the plain crab imperial or casserole-style as the Crisfield Special. You're wasting an opportunity if you order shrimp, lobster or anything fancy such as seafood creole. Stay with the Bay specialties, though I maintain that the crab cakes could still use revamping. And if the prices seem high for eating at a counter or Formica table, try to remember the last time you had fish this good at any price. 8012 Georgia Ave., Silver Spring. 589-1306. L $3-9, D $8- 28. L, D daily. Closed Mon. No credit cards. Beer and wine.