ADAPTING THE recipes restaurant chefs hand out so that cooks can use them at home is not just a matter of reducing the proportions to family size. Or even filling in the missing directions.

And it isn't just guessing what should be done with ingredients that are listed but not included in the direction, or for that matter trying to figure out an amount when none is specified.

Adapting recipes involves a considerable amount of psychology, based on at least a speaking acquaintance with cooking skills. It also involves a lot of leg work.

Knowing this, it's a wonder food writers ask chefs for their secrets. But we do and with enough perseverance and testing, we are often rewarded.

Cheveux d'anges , a pasta dish, and salade d'endive jus de pamplemousse are classic cases. Translated an angel's hair and endive salad with grapefruit juice, these are creations of the fertile imagination of Sal Montezinos, owner-chef of Deja-Vu, a Philadelphia restaurant. Montezinos was more than happy to share his recipes. And true to his promise they arrive in plenty of time for testing. Plenty of time as long as I was willing to devote one entire Saturday afternoon to collecting the ingredients. Considering how much chefs hate to write down recipes, this was a good omen.

The recipes were accomanied by a letter from the restaurant's maitre d'hotel: "Enclosed please find the two recipes you requested. The recipes, however, came to me with specific amounts of ingredients as Sal tends to cook more by feel than exact amounts. This may pose a problem in translation, yet it might be easier to keep in mind that the salad and pasta should be made for four people, in not too large amounts."

So far, nor surprises. Knowing how many people are being served is, of course a great help.

A relatively careful reading of the recipes brought up some questions, so I phoned Montezinos. He assured me it would be difficult to find certain of the ingredients (he was right) but I could make some substitutions, if necessary.

The next step was to figure out where I could by apricot chutney (nowhere, though I could make it myself); orange blossom honey, pink peppercorns and Dutch mustard (Georgetown Coffee Tea and Spice), but Saturday afternoon in the tiny store is like shopping at Loehmann's and besides, they were out of Dutch mustard); enoki daki mushrooms (at the Mikado, but only by chance -- I went there looking for something else); and fresh mint leaves (Hudson Brothers, where I was lucky because they had 8 leaves left in the bottom of the box. While I was there I picked up some arugula, an Italian salad green, because it's hard to find and I thought it might be good with the dressing for the endive salad).

The angel's hair dish refers to the thin pasta on which the sauce is placed. But by the time I had stopped at all of the above-mentioned places, plus two others where I had hoped to buy some of the ingredients, plus the supermarket for the ordinary ingredients, I didn't feel like making a trip to Vace for fresh pasta. I made do with fresh Japanese noodles, though they don't hold the sauce the way the Italian pasta does.

Four hours later the ingredients were laid out on the kitchen counter and it was time to start interpreting. I had already decided I was not about to make apricot chutney so I mixed a little apricot butter in with some mango chutney.

The first directions were easy: "Peel and clean cucumbers of all seeds." But what did the chef mean when he wrote: "Make an extract of the orange blossom honey, pink peppercorns and saffron. Cook the mixture for 5 minutes over a low flame to extract the flavor of the pepercorns and saffron into the honey"? Should the peppercorns be plucked out after? It helped to have eaten the dish because I recalled eating peppercorns.

The cooking instructions said to rub the bottom of the wok with the clove of garlic, but there were no directions for what to do with the garlic after that. It seemed reasonable to mince it and saute it with the shallots and leeks. It also seemed reasonable to cook the cucumbers with all the other vegetables, even though the recipe didn't say that. I also guessed that everything should be cooked in 2 tablespoons of light oil though none was mentioned.

There were no directions for the enoki daki mushrooms, but they really don't need cooking so they were added at the last minute.

I decided not to saute the steamed pasta in butter with salt and pepper, reasoning that this was a restaurant trick for quick heating of already cooked pasta.

The results? Excellent, though it seemed as if the sauce could have used a little more liquid. Montezinos agreed when I called him the next day.

It also turned out that the vegetables were to be sauteed in a mixture of butter and oil; that each vegetable was to be sauteed separately; that the enoki daki mushrooms are added at the end and cooked very briefly. Not too far off, except . . . the Armagnac and Madeira. Armagnac and Madeira?

Montezinos said a tablespoon of each should be added at the end of the cooking, not only for flavor but for liquid.

The salad was a snap, by comparison. Even though there were no proportions given, the dressing is a basic oil and lemon juice, except that the lemon juice is replaced by grapefruit juice, which provides a slight sweetness and softening. Dijon mustard can be used in place of Dutch mustard and if you can't find fresh mint leaves you can reconstitute a few dried ones and use them.

You can also try the dressing on arugula. It's wonderful.

Nine hours after the shopping expedition began, not counting the additional phone conversation with the chef, the recipes were ready. They have been reinterpreted so that you won't have to spend the entire afternoon shopping, but you won't be able to find everything in your local supermarket, either. Just plan ahead a little and pick up the non-perishables when you are in the neighborhood.

On the other hand, a wonderful mussel recipe I picked up in Chicago last fall necessitated only one additional trip -- to the fish market -- and the recipe worked just as the chef had written it. Formerly chef at the 95th, in Chicago's John Hancock Building. Belgian born and trained Willy Maes in now catering. His company? "Chef Will Travel." In Belgium he says, the mussels are served with pommes frites , fried potatoes; in France they are served with parsley potatoes or fresh vegetables. Be sure to serve them with lots and lots of crusty French bread. CHEVEUX D'ANGES DEJA-VU (4 servings) 2 leeks, washed and trimmed 2 cucumbers, peeled, halved lengthwise and seeded 1 bunch scallions, cleaned and trimmed 2 red peppers 2 green peppers 1 small cluster enoki daki mushrooms, washed and trimmed, about 20 1 clove garlic, minced 1 clove shallot, minced 2tablespoons orange blossom honey 2 teaspoons pink peppercorns 4 strands saffron 2 tablespoons tomatoe puree 2 tablespoons mixture butter and oil 1 teaspoon curry powder 1 tablespoon chutney* Salt to taste 2 teaspoons currants poached in 2 tablespoons brandy 1 tablespoon Armagnac or other good brandy 1 tablespoon Madeira 3/4 pound fresh thin pasta

Cut the leeks, cucumbers, scallions and peppers into very thin julienne strips. Cook the honey, peppercorns and saffron together over low heat for 5 minutes; add the tomato puree; set aside. Poach the currents in the brandy for 2 minutes; set aside.

Heat the oil and butter in a wok. Saute the garlic, shallot and leeks in the hot oil for 2 minutes. Add the peppers and scallions and cook 2 minutes longer. Add the cucumbers and cook another minute. Stir in the curry, chutney, salt and honey mixtures. Add the mushrooms, currants, Armagnac and Madeira. Stir once or twice and serve over pasta.

*You can mix 2 teaspoons of apricot butter with 1 teaspoon of any chutney to achieve the apricot flavor.

If you cannot buy fresh pasta, Nontezinos suggests very thin whole-wheat pasta from the natural food store. SALADE D'ENDIVE JUS DE PAMPLEMOUSSE DEJA-VU (4 servings) 4 medium endive 2 well-flavored firm apples 1 1/2 to 2 teaspoons Dutch or Dijon mustard 3 tablespoons fresh grapefruit juice Salt and freshly ground black pepper to taste 2 tablespoons safflower oil 2 tablespoons soy oil 2 finely chopped mint leaves

Wash the endive. Whisk the mustard with the grapefruit juice, salt and pepper until the mixture is light. Beat in the oils, whisking as they are added. Cut off the ends and head of the endive and cut endive into julienne strips. Mix the endive and apple and cover with dressing immediately so that apple does not turn brown. Sprinkle with chopped mint and serve. MUSSELS WILLY MAES (4 servings) 6 pounds mussels, washed and scrubbed 1/4 cup chopped shallots 1/2 cup finely sliced leeks 1 teaspoon pepper 2 cups dry red wine 4 tablespoon sweet butter 1/2 cup chopped parsley

Place the shallots, leeks, pepper and wine in a pot large enough to hold the mussels, bring mixture to a boil. Add the mussels and cook for 5 minutes, or until the mussels open. (Discard any mussels which do not open.) Remove mussels and keep warm. Bring the liquid to a full rolling boil for 4 or 5 minutes. Add the butter, a few small pieces at a time, shaking the pot. Add the parsley and serve over the mussels in individual bowls.