Fish, having become nutritionally chic precisely when we can't afford it so often, remains slightly unfamiliar territory for many. But while many fish stores do nothing to overcome a common fear of fish shopping, some take the lead in labeling their fish with names and prices, in encouraging us to special-order monkfish or eel. When the thought of chicken fills you with ennui, and frozen fish fillets fail to make your juices run, turn to the accompanying directory of local fish stores. If you're in a porgy and a croaker rut, branch out. Wrap a white fish fillet around an oyster stuffing, for an elegant alternative to a roast beef dinner. Or steam sea bass in a Chinese black bean sauce with less effort than it would take to make meat loaf. Meanwhile, learn the rules for fish shopping, to stretch your fish dollar and assure yourself of freshness and quality.

SEAFOOD prices vary enormously in local stores -- as much as $6.50 per pound for a large size (low count) of shrimp, for example. But high prices should not turn you off a store, necessarily. Shops like Cannon's and Chevy Chase Seafood charge alot not only because they pay high overhead but also because they carry first class fish.

Unusually low prices on advertised items should not turn you off, either. Lower prices, says wholesaler/retailer Steve Himmelfarb of U.S. Fish, are usually an indication that supply exceeds demand on a certain item. So the smart consumer will take advantage of a temporary abundance of a certain species, buying salmon in the fall, bluefish in the spring and fall, flounder fillets in the warm weather months (except for a traditional "dry" spell in August), and so forth. Right now, rockfish and bay scallops are a good value. Fish don't disappear when the seasons change -- fishing them just gets tougher in bad weather. You can get most types of seafood year-round, but you'll just pay more for them off-season. To the extent that you shop for price and variety, the directory to local fish stores on pages E6 and E7 should give you an idea where the fish are and what you'll be paying for them.

HOW TO BUY FISH

Fish that tastes "fishy" is usually either overcooked or not fresh. The best way to assure freshness is to patronize a reliable fish shop, and to look for these signs:

* Bright, clear, bulging eyes. Contact with ice may make the eyes cloud over, but they should not be sunken nor contain traces of blood.

* Reddish gills. As fish age, gills change to pink, then gray, then brown-green.

* No unpleasant fishy smell, although there may be a mild sealike aroma.

* Firm flesh that springs back when you press it and doesn't separate easily from the bone. If a whole fish is limp and floppy when you pick it up, pass it by. Scales should be bright and shiny, and stick tightly to the skin. Skinless fillets should have no slime covering the surface.

DECIPHERING THE LINGO

Depending on how big the fish is, it will be marketed in one or more forms:

* Whole fish: as it comes from the water, though it's often scaled and gutted (drawn).

* Whole dressed: a whole fish scaled and gutted, with the fins removed.

* Pan-dressed: a whole cleaned fish with the fins, head and tail removed so the fish will fit easily in a pan.

* Steaks: cross-section cuts of large fish such as cod, halibut, salmon, shark or swordfish.

* Fillets: boneless (and often skinless) sides of fish that have been cut lengthwise from the backbone.

* Butterfly fillets: two fillets cut away from the backbone but joined by the belly flesh, so they make one large double portion.

* Sticks: slices cut from fillets or steaks.

If you have the fish pan-dressed, don't hesitate to ask the dealer for the fish's head and bony carcass to make soup or stock. Fish stock freezes well and comes in handy for poaching or making seafood soups.

HOW MUCH TO BUY

Allow 1/2 pound and maybe even more of edible flesh per serving. This means about at least 1/2 pound of fillet, slightly more for steaks, 3/4 pound of pan-dressed fish and 1 pound of whole fish per person.

REFRIGERATING FISH

Ideally, fish should be eaten right after you catch or buy it. If it is not to be eaten immediately, cover it loosely with moisture-proof paper or place it in a covered dish in the coldest part of the refrigerator and eat it within a day or two.

FREEZING FISH

Joan Cone, in "Fish and Game Cooking," offers a secret for freezing fish which involves a protective dip made of lemon juice and gelatin, and works with whole fish, steaks or fillets:

Stir 1 envelope (1 tablespoon) unflavored gelatin into a mixture of 1/4 cup fresh or reconstituted lemon juice and 1 3/4 cup cold water. Heat over low flame, stirring constantly, until gelatin is dissolved and mixture is clear. Cool to room temperature. Dip the fish into this lemon glaze and drain for several seconds before wrapping individually in a heavy-duty plastic wrap. Then place within heavy-duty plastic freezer bags for double protection, marking the date and exact contents on the bag. Most fish shouldn't be kept frozen more than a month or two.

COOKING TIMES

The Canadian Department of Fisheries devised a rule-of-thumb that simplifies fish cookery. No matter what the "cut" of fish (whole, steaks or fillets), or how you are going to prepare it, a fish is cooked proportionate to its thickness. Measure the fish at its thickest point (lying on its side, you measure the depth, not the width, of the fish), and cook it 10 minutes per inch, 5 minutes per half-inch, etc. -- at 350 to 375 degrees if you are baking it. Always bake fish in a pre-heated oven.

If the fish is covered with sauce or wrapped in foil, allow an extra 5 minutes per inch. If the fish is frozen, double the cooking time, and don't thaw the fish before cooking it. When cooking rolled fillets, measure the diameter of the rolled fillets. If you are baking stuffed fish, measure the depth of the fish once you have added the dressing, and bake at 450 degrees. If the fish is to be poached, bring the liquid to a boil, add the fish, lower the heat, and then start counting the time.

BARGAIN BOOKS

Among the best local buys in seafood cookbooks are two nicely illustrated "Maryland Seafood Cookbooks" published by Maryland's Seafood Marketing Authority and widely available in local fish markets and bookstores. Book 1 ($1.50) presents 68 recipes, mostly traditional methods for preparing shellfish. Book 2 ($2.95) contains 102 recipes, mainly from Maryland seafood restaurants (compare versions of crabcakes and crab imperial), plus a 12-page insert on how to fillet, shuck, clean, dress, freeze and eat Maryland fish and shellfish.

Among shellfish cookbooks, a niftly little package called "the Craft of Dismantling a Crab" by Robert H. Robinson illustrates how to open clams, lobsters, oysters, mussels, whelks and various kinds of crab. )$4 from Sussex Prints, Box 469, Gerogetown, Del. 19947).