THE NATIONAL barbeque season has begun. Out come the grills, the mitts, the long-handled forks, the charcoal and the fire starters. Out come the steaks, hamburgers, frankfurters and chickens. Unfortunately, most of us are missing one of the best opportunities in outdoor cookery. How about grilling a fish? Do so and you will end up with moist, crisp, crunchy skin covering tender flesh.

You could hold your fish over the heat with an ordinary hinged hamburger grill, but there's a real danger that the delicate flesh of the fish will be crushed by the pressure exerted by the flat grill bars. The specially shaped fish grills are well worth their cost. The enlongated shape and curved, closely set wires of the fish grills are designed to cradle the entire body of the fish without breaking it.

The classic fish-shaped grill is made of tinned steel that will not interact with any food. The grill portion is 20 inches long. It consists of a rectangular frame slightly bowed at the center to accommoddate the bulge of a fish. Curved wires above and below will support and hold firm the contents. Near each corner of the frame are 4 1/4-inch legs. Four of these legs go down and four go up.

The eight-leg system allows you to flip the grill over at the mid-point in your cooking and still have the tool resting firmly on its feet above the heat source. The legs are loop-shaped so you can slip the handles of two wooden spoons through them to easily remove the grill and its contents from the coals. The legs and a 5-inch handle are sturdily welded to the body. The entire device swings open to accept the fish.

The front and back ends of the grill are blunt, which will allow it to hold a large fish with the head and tail removed. The legs are narrow at the bottom, which makes it easy to settle them into the coals of your fire. The retail price is about $20.

There is a similar model being made and imported into the United States. The unit has two sets of folding rectangular wire supports instead of ridged legs described above. The theory behind the design was that the collapsible supports would be a boon to those with limited storage-space at home or to campers and fisherman who wish to travel with the grill. Good theory, bad execution. These grills are unsatisfactory. The hinged legs are very difficult to get into the coals in the first place, and when it comes time to flip the grill over, it's virtually impossible to give the wire supports a firm footing before they collapse.

A number of shops also carry individual fish grills. Made of tinned steel, the most common model is 18 inches long and 3 inches wide. A good size for smaller fish, it is not very convenient for group barbeques. It operates on the same principle as the hinged hamburger grill, but the sides are made convex to accommodate the prompt, delicate body of a fish without crushing it. A separate ring-shaped fastening holds the handles together, keeping the grill closed while you turn the fish. This grill is footless and you will therefore, need some system for holding it above the coals.

If you're using an outdoor cooking system with its own grillwork, you can rest this fish grill on top; if not, you will be forced to devise some system of your own. I will not be giving the "Well Thought-out Design" award to this tool.

Whichever fish grill you choose, the technique for use is simple. Rub the fish with herbs. Leave the head and tail intact. (This will give you a moister fish.) Give the body of the fish a few shallow, diagonal slashes on both sides to prevent it from curling up during cooking. Lightly grease the wires of the grill to prevent the delicate skin of the fish from becoming stuck to the hot wires. The fire should be low, and it is important to prevent flare-ups. When the first side is done, flip the entire grill to cook the other side.

Good fish grills are of simple, but sturdy manufacture. They come in a range of sizes for just about every commercial fish. Choose one that will accommodate the size fish you will be cooking most often. Make the decision by estimating the number of people usually served, eight in my case. Each diner will require about one proud of whole fish (estimate half pounds per person for fish fillets). I then ordered an eight-pound fish from my fish dealer and used that fish's measurements to guide my grill purchase.

It's a somewhat cumbersome process, but it's important to remember that too small a grill will crush the fish and too large a grill will fail to give proper support. The fish will break up during the flipping. The proper size fish grill will give you a great deal of pleasure for your money.