A fish you have caught yourself always seems to have a more exquisite flavor. If you carry this one step further, and head for the sea with the idea of seeking out and catching fish for a specific purpose - the makings of a classical seafood fish - then you have the start of a beach meal that will be recalled years later at other beaches and other parties.

The dish worthy of such an effort is bouillabaisse, a beautiful-to-behold, fabulous tasting, saffron-kissed fish soup. It is an artful blend of flavors with as many versions as there are fishing villages along the Mediterranean coast near Marseilles, where it originated.

For those who say, "I don't go to the beach to cook," I can only say that making bouillabaiss by the sea with fish you have caught has nothing to do with everyday cooking.

While the recipe will accept many variables, there are a few constants. A real bouillabaisse must have fresh fish and shellfish, several kinds; fresh fish broth; tomatoes, onion, garlic - handsful of garlic - leeks, fennel and saffron. The total experience requires the accompaniment of garlickly French bread, a few boiled potatoes, and a nice, dry, rose wine. That's right, pink, not white.

Advance planning for a bouillabaisse party helps. We take to the beach some of the basic ingredients without the foggiest notion whom we will entertain. Finding the guests becomes almost like finding some of the ingredients for the recipe.

Since there is work involved, this should be a shared creation. After all, the hostess is on vacation. You can assign the family fisherman, or even potential guests, to do some custom-catching of fish for the soup. Lacking fisherman, you will have to rely on the local fish market.

The actual cooking of bouillabaisse is not beyond the scope of the average cook. It is more a matter of collecting and assembling ingredients, almost like a jigsaw puzzle. That's why it helps it divvy up the jobs.

Making the tomato sauce base is time-consuming. But it can be done at home, frozen and transported to the beach. Certain necessary ingredients should be purchased at home to save long searchers in unfamiliar stores.

Our version of bouillabaisse was learned from Robert Greault, owner-chef of Le Bagatelle restaurant. Several years ago he taught a one-lesson crash course in bouillabaisse for anyone with two hours and $10. It turned out to be one of my best investments. Not only for the bouillabaisse, which is a once-a-year recipe, but also for Greault's garlic bread. That alone could make anyone a star in the kitchen.

There were more peeled garlic bulbs tossed into the bouillabaisse than some cooks use in a year. Each time more garlic went in, the students would gasp.

But every myth and murmur of the sea came alive with the first spoonsful of the red-orange broth, white fish chunks, pink shrimp and golden mussels in black shells.

This is not a budget recipe. Made in a city kitchen and buying the fish and shellfish will cost roughly $2.60 per serving for just the soup. Made at the beach using fish you have caught, the soup will be about $1.50 per saving.

However, vacationers who eat out frequently, find they pay nearly that for fast food meals. The party could make you look the soul of thrifty virtue, depending on who's been picking up the restaurant checks. BOUILLABAISSE (12 servings) Seafood: 7 to 8 pounds fish fillets, at least three of four varieties of firm and soft fish: rockfish, red snapper, flounder, sea bass, spanish mackerel (don't use bones); blue fish (don't use head); and eel, when available. Just as satisfactory will be any very freshassortment of common catches from a pier - spot, mullet, porgies, sea trout etc. 1 dozen cherrystone clams 2 pounds mussels 1 dozen shrimp 1 live lobster, if available. If not, add another dozen shrimp.

Cut fillets into diagonal pieces.

Scrub and soak clams in cool, salted water, changing water several times in 2 hours to allow clams to expel sand. Discard any that are broken or not tightly closed.

Scrub and soak mussels, pull of beards. Soak 2 hours or overnight, adding 1 tablespoon flour per quart of water. The mussels literally fatten up on the flour and purge their grit. Discard any that flaot.

Kill lobster by severing spinal cord. To do this, place the lobster on its back and insert the tip of a sharp knife between the body and tail sections and make a quick downward cut. The split lengthwise, removing the stomach and intestines under the eyes. Save the red coral roe and green stuff called tomalley for use when lobster is combined with other ingredients. Divide the lobster into 12 pieces and crack claws. TOMATO SAUCE BASE (Can be made in advance, frozen.) 5 large fresh tomatoes, or 2-pound can. (Peel and seed fresh tomatoes and reserve for fish broth) 1 bunch of leeks (about five) white part only, chopped (Reserve green part of fish broth) 1 1/2 large onions, finely chopped 1/2 cup garlic cloves, finely chopped 1 cup olive oil 1 teaspoon saffron 1/2 teaspoon salt 2 bay leaves, crushed 1 teaspoon thyme 4 (rounded) teaspoons tomato paste Freshly ground black pepper

In large skillet, heat olive oil, add leeks, saute several minutes until soft. Add onions, garlic, saffron, salt, bay leaves, thyme and continue cooking gently for about 15 minutes. Add tomato paste, black pepper, tomatoes, and simmer 15 minutes, stirring occasiionally. FISH BROTH 3 quarts cold water Fish heads and bones left after filleting, washed thoroughly 1/2 large onion, sliced 3 leeks, green parts only, chopped 1 stalk celery Large handful of parsley 6 to 8 peppercorns 1 1/2 tablespoon salt 2 large cloves of garlic, flatten with knife 1 teaspoon fennel seed, or 4 or 5 dry stalks 2 pieces of lemon peel Junice, peel and seeds of tomatoes used in sauce

Add ingredients to cold water and bring to a boil. Simmer for 30 minutes after it comes to a boil. Remove from heat. Allow to settle and clarify.

Final assembly and cooking:

Two 5-quart, wide, low pans are handsome for final cooking and serving. But a 10-quart soup kettle will do nicely.

Coat pans with olive oil, split the thawed tomato sauce between the two pans, and heat to a simmer. Place fish slices, skin side up, over tomato mixture in both pans. Salt and pepper fish.

Place clams, mussels, shrimp and lobster on fish. Strain fish broth carefully over fish and shellfish, dividing evenly between the two pans. Cover and cook gently until fish flakes easily, and clams and mussels are open. Mix gently with a fork so the firm fish chunks will stay intact. (Soft fish will disintegrate. Don't worry, they are supposed to.)

Taste. Salt and pepper if necessary. Sprinkle with freshly chopped parsley for garnish. Serve from pots on stove, or bring pans to table, keeping one hot until the first is empty. Have garlic bread and rouille on the table. GARLIC BREAD (2 to 3 slices per person)

Chef Greault uses small loaves of French or Italian bread sliced diagonally in one-inch thicknesses. The slice bread is toasted on both sides on cookie sheets under the oven broiler. After toasting, each slice is rubbed on both sides with a peeled clove of garlic. The crisp bread acts like sandpaper, shoving garlic lavishly into the pores of the bread. Good olive oil is poured on a plate. Each slice of toast is dipped briefly into the oil. This is garlic bread. ROUILLE (Garlic mayonnaise) 1/4 cup garlic cloves 1/2 teaspoon tomato paste Pinch of saffron Dash of cayenne pepper

Crush the above ingredients together to make a paste. Use mortar and pestle.

Add 1 cup homemade mayonnaise, mix well, salt if necessary. Serve in a bowl to be spreadon garlic bread or added to the broth.