The beauty of stock is not self-evident People -- even people who cook a lot -- sometimes have to be talked into thinking it's important. And if they do realize the value of making this homely sounding stuff, it's sometimes an abstract realization that never gets put into practice.

When the subject comes up they act sheepish, as if you'd asked them if they get enough exercise or always remember to floss. "I keep meaning to," they say. Or, "I would, but I just don't have time." Or even, "I forgot."

Stock, in and of itself, is not particularly appealing. Its natural-born flavor is not anything to write home about and there's not much you can do with it unadorned.

But the simple truth about stock, especially veal stock, is that it is the single most valuable ingredient in any kitchen where good cooking goes on. It's not for nothing that the French call stocks "les fonds" or "the foundations."

When the uninitiated hear the word "stock" they automatically think of soup. But in fact, while stock is a useful ingredient in some soups, and some soups are really nothing much but stock, there are other things to do with stock that make real magic.

First among the magical things are those exquisitely flavored, richly colored little sauces that help draw you to fine restaurants. It's these sauces that turn a plain piece of roasted or saute'ed meat into a chef's reputation. When they are perfectly balanced and treated with originality they are masterpieces, and that's what good chefs get paid for.

These magnificent "little" sauces are most often nothing but stock, usually veal stock, boiled together with pan drippings and flavorings such as garlic or herbs, until it has "reduced" in volume and thickened on its own into a sauce.

Of course not everybody, even with the best ingredients, can produce a sauce worthy of Le Pavillon or Jean-Louis. But give a novice cook a piece of meat, a few herbs or other flavorings, some good veal stock and about a minute of instruction, and what he or she can produce will be much closer to the heavenly than to the mundane.

In other words, it's veal stock, made once every couple of months and kept frozen, that makes the difference between a fried pork chop and an interesting, elegant dish that you could be proud to serve to your fanciest company.

As a sauce base, veal stock is the most versatile of the stocks, light enough to be compatible with chicken and veal and substantial enough to go with pork, beef and lamb. If it's made with the right kind of bones, it will have enough body to thicken by itself without flour or cornstarch.

Beef stock is much less useful because it is too strong, especially when reduced, to be matched with anything but beef. And, because they come from mature animals, beef bones lack the gelatinous quality that makes veal stock so rich and easily thickened.

Chicken stock is useful as a sauce base, too, in the same way veal stock is. But it's useful only with chicken or other mild-flavored fowl, and it will lack some of the body that well-made veal stock has.

Stocks can be used simply for deglazing pans in which you have saute'ed or roasted meats or fowl. The technique is just to add a couple of tablespoons of stock to the hot pan, over heat, boiling and scraping up all the good bits that would under other circumstances be consigned to the sink or the dishwasher. What you'll have is a bit of very flavorful sauce.

But both chicken and veal stocks have uses other than reducing them to make wonderful sauces. Chicken stock is often used as a flavorful but not too assertive liquid base for pure'ed vegetable soups. And chefs whose operations can afford it sometimes poach chicken breasts in chicken stock, then reduce this resulting double stock to make a sauce. Chicken stock is also a part of nearly every Asian stir-fry dish.

Veal stock is also the braising liquid of choice for vegetables, particularly those that will be served with meats. It's an integral part of gratin dauphinois, the well known "scalloped" potato dish of France, and of braised carrots, onions, fennel, spinach and, lately, the meltingly sweet braises of shallots and garlic used almost like marmalade as accompaniments to simple meat dishes.

It can also, in a pinch, be used as a medium for "saute'ing" by those who must reduce their fat intake. While it won't produce real saute'ed food, it will add color and flavor similar to that achieved by real saute'ing in fat.

Finally, veal stock can be used anywhere you need a shot of flavor. The American Cafe restaurants, for instance, claim that one of the reasons their chili is so good is that it's made with veal stock. You can add it to blah soups, to regulation turkey gravy, to almost anything to which you would ordinarily add a little water. You can also use it as the liquid ingredient in Asian stir-fry dishes, although chicken stock is more usual. Building on the Foundation

Mastering a few basics of making sauces from stock will give you the ability to produce a truly wonderful dish at a moment's notice from fairly mundane ingredients.

Say you've saute'ed some small pieces of meat in a frying pan. After you've finished, you put the meat aside and keep it warm. If you want to keep things really simple you'll then add anywhere from 1/2 to 3/4 cup of stock (depending on the size of the pan) to the pan and let it boil while you scrape up all the brown bits. When the stock is reduced by about half, that is, when it's about half its original volume, it will probably be thickened into a sauce.

You can then add enrichment in the form of butter (added piece by piece to the center of the boiling stock) or heavy cream. You will have added a lot of calories (well defatted stock has a negligible calorie count), a lot of fat, and a lot of flavor and smoothness.

If you want to be a bit more complicated and add more flavor, you can do this: After the meat is removed from the pan, pour out the fat and add a little butter if the fat looks or smells burned. Otherwise use the same fat. Add a few finely chopped cloves of garlic, some minced scallion or yellow onion, finely chopped shallots, even mustard. If you have fresh herbs, you can add whole stems now and strain later if you want to.

Let these saute' gently a few minutes, then deglaze the pan with stock, or with wine, cognac or sherry vinegar (especially with fowl), add stock and reduce it. Other flavorings you can add as the stock is boiling are tomato paste, herbs, anchovies, green peppercorns or spices. Be careful with highly flavored things like anchovies, however, because all flavors will intensify as you reduce the liquid.

You can also enrich this slightly more complex sauce with butter or cream.

Then there is the technique known as tomber a glace, which sounds formidable but isn't. The idea is to brown any extra bits of meat and bone such as the nonfatty trimmings from roasts.

On whole veal and lamb loins there are "belly flaps" comparable to the flank steak on beef that are ideal for this. You could use the shank end of a leg of lamb or the trimmings from a pork roast. Meat and bone should be in relatively small pieces and they should be as fat-free as possible.

Let the little pieces brown, in butter, until they are very richly colored. If you don't brown them well enough, your end product will be anemic looking. Then, still over heat, add 1/2 cup of stock and let it boil gently, scraping up brown bits and stirring constantly, until it is reduced almost to a glaze.

Add another 1/2 cup of stock and again let it reduce to a syrupy glaze. You'll end up with a little more sauce this time. Repeat this procedure with as much stock as you want, reducing it each time until you wind up with as much exquisitely rich, thick sauce as you need.

It is possible to over-reduce a sauce, which will result in a bitter, slightly "bony-tasting" sauce. This usually happens only when you let the finished sauce simmer at length after it's already been sufficiently reduced.

Tomber a glace is a classical technique revived by today's chefs to produce ultrarich, highly flavored sauces with no added thickener. Add your own signature flavorings and you will have a dish that the finest, most expensive restaurant would be proud to serve. Stocking Up

Stocks are nothing but uncooked meaty bones, a few flavoring vegetables and water, simmered slowly together until the solid ingredients have rendered all their flavor to the water.

Vegetables for both veal and chicken stock are onions, carrots, celery and sometimes leeks. They do not need to be peeled or scraped, only washed. Both benefit from the addition of a "bouquet garni," which consists of a few parsley stems, a few thyme sprigs and a bay leaf. You can wrap it all in cheesecloth, tie it together with the parsley stems or enclose it in a long piece of leek that has been slit on one side and then tied together with string.

Stocks are never salted, since they may end up being highly reduced and the saltiness therefore greatly intensified.

In veal stock the bones and vegetables are browned first so that the final product will be richly colored. Chicken stocks are usually made with unbrowned solid ingredients.

In general, the smaller the pieces of solid matter, the shorter the browning time and the shorter the simmering time. Other than that, the size of the bones and vegetables doesn't matter.

As the stock simmers, skim fat and scum from the top. Most will rise to the surface at the beginning of cooking. If you don't do this, the stock may taste greasy.

After the stock has finished simmering, you'll need to strain it, then cool it quickly. Since well-made stocks jell when they are cold, it's important to strain them while still warm. Do this through a hard colander, since you want to press hard on the cooked ingredients to wrest as much flavor from them as possible.

Stocks are highly perishable and should be cooled as fast as possible to reduce the risk of spoilage. Leave the pot uncovered while it cools or the stock may sour. The best way to cool a stock quickly is by dipping the hot pot into a sinkful of cold water. Don't put hot pots full of stock into the refrigerator, since all you'll achieve is heating up the other contents.

Stocks will keep for several days in the refrigerator, but it's best to boil them hard for several minutes before reusing to kill any bacteria that may have grown in the meantime. Never leave stocks sitting around a warm kitchen.

Stocks freeze well. After they've been strained, cooled and completely defatted (any fat remaining in the finished stock will have risen to the top and hardened), stocks can be frozen, covered tightly, in Styrofoam cups. Large quantities of cups and covers are available in all restaurant supply houses. You can also freeze stock in ice cube trays and then store the frozen cubes in plastic bags. You'll soon learn what quantity is most useful to you.

Stocks used for making sauce or for braising can be used directly from the freezer.

You can also reduce veal stock until almost all its liquid content is evaporated, producing a hockey-puck-like mass called glace de viande. To make glace de viande, boil finished veal stock until it is reduced by about half. Then strain it again (little specks of solid matter may have appeared), and boil again until you have 10 to 15 percent of the volume you started with.

Glace de viande is tricky to make because it burns easily toward the end of its cooking. Sniff it frequently as it begins to get syrupy.

Glace de viande keeps for weeks in the refrigerator. Bits of it can be reconstituted into stock by adding very hot water or it can be added in tiny spoonfuls to soups and sauces to "punch up" their flavor.

Here are recipes for both veal and chicken stock, plus some ideas for using them: VEAL STOCK (Makes about 3 quarts)

You can make veal stock in any quantity, but it's sensible to make as much as you can at one time. If you want to hurry the process, have the bones cut into pieces by the butcher, and halve or quarter the vegetables. The following quantities can be adjusted to suit your needs or the size of your pot. 4 to 6 pounds meaty veal bones, mostly knuckle or breast if possible (veal breast makes the best stock, but it's expensive) 2 yellow onions, with peel, halved 1 carrot 1 stalk celery 2 leeks, very well washed (optional) 2 to 3 tablespoons tomato paste (optional) Several parsley stems 2 branches fresh thyme or 1/4 teaspoon dried 1/2 bay leaf

Brown the bones, after removing all visible fat, by arranging them in a single layer in a shallow roasting pan and letting them roast in a 400-degree oven until very brown but not burned. This could take anywhere from 45 minutes for smaller pieces to 2 hours for bones left very large. Vegetables should also be browned. Add them to the meat so that they can spend about an hour in the oven. Vegetables don't need to be peeled, only cleaned.

When all is well browned, remove from oven. Put meat and vegetables in a large pot, preferably one that is taller than it is wide in order to minimize evaporation. Pour all the fat from the roasting pan.

Tomato paste is an optional ingredient that adds color and a small bit of flavor to the finished stock. If you want to use it, put the roasting pan over medium-high heat and add tomato paste. Stir it, scraping up brown bits of meat and vegetables, until the tomato paste begins to darken.

If you don't use tomato paste, simply add a cup or so of water to the pan and boil, scraping up brown bits. Pour contents of roasting pan into stockpot. Rinse pan thoroughly with water to get out all the flavorful bits, emptying water into the stockpot. Add enough cold water to cover solid ingredients by about an inch.

If you are using dried thyme, enclose parsley, thyme and bay leaf in a double square of cheesecloth, tie securely and add to the pot. If using fresh thyme, simply tie these ingredients together with a parsley stem.

Bring contents of the pot to a simmer over medium-high heat, skimming fat and scum that rise to the surface. Reduce heat and let the stock barely simmer, uncovered, for 6 to 10 hours, depending on the size of the bones. Skim occasionally. There should be very little evaporation at the end of cooking time.

Strain well, degrease and cool quickly. Then refrigerate or freeze. CHICKEN STOCK (Makes 1 1/2 to 2 quarts)

Chicken stock is generally made in smaller quantities than veal stock. Two whole chicken carcasses should produce about a quart of stock, but you can make less than that if you want to. Use any part of the chicken except the heart or the liver, as they will make the stock bitter. 2 parsley stems 1 branch fresh thyme or a pinch dried thyme 1/2 bay leaf 2 raw chicken carcasses, chopped, or an equivalant amount of raw chicken parts 1 onion, peeled and quartered 1/2 carrot, sliced roughly 1/2 celery stalk, sliced roughly

Tie fresh herbs together with a parsley stem or enclose herbs in cheesecloth and tie (if you are using dried thyme).

Put all ingredients in a kettle, preferably taller than it is wide. Cover with cold water and bring to a simmer over medium-high heat. Reduce heat so that stock barely simmers, skimming frequently at the beginning of cooking time.

Let stock simmer for 2 to 3 hours, then strain, degrease and refrigerate or freeze. The meat should have rendered all its flavor and should probably best be discarded. MEDALLIONS OF PORK WITH MUSTARD SAUCE (2 to 4 servings, depending on rest of menu) Chicken pieces can be substituted for the pork. Salt and pepper to taste 4 boneless pork chops, cut from the rib or loin, about 3/4-inch thick 2 tablespoons butter 1/2 teaspoon dried thyme, or 2 or 3 branches fresh thyme 1 large shallot or 2 scallions, finely chopped 2 tablespoons dijon mustard 3/4 cup veal stock 1/3 cup whipping cream Salt and pepper pork chops. Melt butter over medium-high heat in a skillet just large enough to hold the pork chops. Saute' chops on both sides until they are well browned. Add thyme. Cover the skillet, lower the heat, and let chops cook slowly just until juices are no longer pink.

Remove pork to a platter and keep warm. Drain most of the fat from the pan. Add shallot or scallions and let them saute' just until softened, 3 to 5 minutes. Add mustard to the pan and let it cook briefly, stirring.

Add veal stock gradually to the pan, whisking constantly. Raise heat and let the stock boil while you scrape all the brown bits from the bottom of the pan. Cook the stock until it's reduced by about half. Add the cream and let the sauce boil for a few minutes, whisking constantly with a wire whisk.

Remove thyme branches if you have used fresh thyme and pour sauce over pork to serve. AIGUILLETTES D'AGNEAU A LA BATELIERE (6 servings)

This recipe produces small portions to be presented on individual plates. Plan to serve colorful vegetables with it, and also a "bouquet" of watercress. 1 saddle of lamb, as large as possible 6 tablespoons butter 1 1/4 cups veal stock 1 to 1 1/2 teaspoons extra-strong dijon mustard 1 large garlic clove, chopped fine 1 1/2 tablespoons parsley 2 anchovy fillets, rinsed and mashed 1/4 teaspoon finely grated fresh lemon rind 1/4 teaspoon finely grated fresh orange rind Salt and freshly ground pepper to taste

Bone or have the butcher bone the saddle into 2 sirloin strips and 2 tenderloins free of fat and gristle. Cut the sirloin strips into two 3 1/2-inch pieces. Do not cut the tenderloins.

Heat 2 tablespoons butter in a large skillet. Add the pieces of saddle and saute' over medium-high heat. Turn and saute' on the other side. Add tenderloins at this point, rolling them around to let them brown briefly.

Lower heat and let the lamb cook for a few minutes until it is medium-rare. Timing depends on how thick the lamb is, but you can test doneness by poking with a finger. Medium-rare lamb feels firm but still springy, like the flesh between your index finger and thumb when your hand is rolled into a fist but not clenched. If anything, err on the side of underdone, as the lamb will continue to cook slightly as it sits.

When the meat is done, remove it to a platter and keep warm.

Add the stock to the skillet, over heat, and let it boil while you scrape up the brown bits. Boil until it's reduced to about 3/4 cup. Add the remaining 4 tablespoons butter while the stock is still boiling.

Off heat, add the mustard, garlic, parsley, 1 anchovy and the grated lemon and orange rinds. Taste for seasoning, adding the second anchovy and salt if needed. Pepper if desired.

Slice the pieces of loin and the tenderloins lengthwise into 1/6-inch strips and arrange in a fan pattern on 6 hot plates. Top with sauce and serve promptly. From "In Madeleine's Kitchen," by Madeleine Kamman, Atheneum, 1984 BRAISED FENNEL (4 to 6 servings) 4 fennel bulbs 2 tablespoons butter 8 to 10 cloves garlic, unpeeled 3/4 cup veal stock Salt and pepper to taste

Trim fennel bulbs: remove tough part of root end and branch ends beginning just above where branches meet bulb. Remove any tough, stringy outer layers.

Halve small bulbs lengthwise; quarter them if they are extra large.

Heat butter in a heavy skillet and add fennel and garlic cloves. Saute' them over medium-high heat until they show signs of browning. Add stock, salt and pepper to taste. Lower heat, cover the skillet closely and let all simmer together until fennel is very tender and stock is almost absorbed.

Discard garlic cloves if you want to, or serve them with the fennel, to be spread on pieces of toasted country bread. GRATIN SAVOYARD (4 servings) 1 1/2 pounds boiling potatoes 1 clove garlic, split in half 3 tablespoons butter 1/2 cup swiss-type cheese, grated 3/4 cup hot veal stock

Choose an ovenproof dish large enough to hold the potatoes in a layer about 1 1/2 inches thick. Rub the inside of the dish all over with the cut surfaces of the garlic, then discard the garlic. Butter the dish generously.

Peel the potatoes and slice them thin. Put half the potatoes in the dish, making an even layer. Spread half the cheese over the potatoes, then dot with half the remaining butter. Add the rest of the potatoes, the rest of the cheese and the remaining butter.

Pour stock over all. It should be just about even with the top of the potatoes.

Bake the gratin at 425 degrees until the potatoes are cooked through, the stock is nearly all absorbed and the top is browned, about 25 minutes. LEEK AND POTATO SOUP (6 servings)

Leek and potato soup is simplicity itself to make, and can serve as the main dish in a winter supper. You can vary the amount simply by sticking to the same proportions: approximately equal parts potatoes and leeks, with enough chicken stock to cover. 2 cups baking potatoes, peeled, chopped 2 cups leeks, white part only, chopped 2 tablespoons butter 4 cups chicken stock Salt to taste 1/4 to 1/2 cup whipping cream (optional) You will need equal parts (by volume) of chopped white part of leek and peeled chopped baking potato. Soften these in a heavy pot over medium heat in just enough butter to keep them from sticking.

Add enough chicken stock to cover. If you've used 4 cups of vegetables, you'll need about 4 cups of stock. Add salt to taste, and let the vegetables simmer until they are very tender, about 25 minutes.

Pure'e the soup through a food mill or in a food processor or blender. Return the soup to the pot to heat through, adding whipping cream for a richer soup.