PROFESSIONAL chefs tend to carry their knives around the way other people carry wallets. In the world of cuisine, knives are taken personally, more as extensions of the owner's hand than as something just for slicing the salami.

In "When French Women Cook," Madeleine Kamman tells the story of her apprenticeship in the Michelin-starred kitchen of her Aunt Claire. Aunt Claire, Kamman says, "must have known how I so wanted my own knife, for on my twelfth birthday I received from her my first Sabatier and a sweet little kit of pastry nozzles; both have graced my cooking classes. I have noticed, not without emotion, that every year there is a student chef who starts a love affair with that knife. I have been tempted to give it away, but who would want to give away such an amulette? . . ."

The "chef's knife"--sometimes called the cook's knife--is the one absolutely indispensable knife. It comes in various sizes but the shape remains the same. The blade is more or less triangle-shaped with a cutting edge very gently curved so it can be rocked back and forth against the cutting board. The classic method for chopping is to repeatedly lift the handle up and down while the tip of the blade is anchored with the other hand, or held against the chopping surface. In large knives the weight of the blade does most of the work.

Madeleine Kamman's first Sabatier was undoubtedly made of carbon steel, but in the United States in 1983 we have more choices to make. Carbon steel (that is, steel with a high carbon content) is soft and flexible as metals go, so it takes an edge magnificently, but it also rusts and stains. Alloys added to make the steel stainless also make it harder and therefore more difficult to sharpen. To confuse the story even further, many knives on the market are called "high-carbon stainless steel," which is meant to imply that there are enough alloys in the steel to make it stainless, but not so high a level as to render it impervious to sharpening.

Knives made of pure carbon steel can easily be kept sharp at home and therefore require professional sharpening much less frequently. They have more give than stainless knives, and to some cooks feel more maneuverable. But if neat appearances are uppermost in your mind, forget carbon steel. There is no way in the world, despite vows of diligence, to keep a carbon steel knife spotless. It is going to look stained and grungy most of the time. If you lay it down for a minute between chopping the celery and chopping the onions, the onions are apt to have a few dark streaks. But the darkening will not kill you; in fact, if you should happen to eat such a darkened onion, you'd only be getting a little extra iron in your diet.

The degree of hardness of a stainless knife is unfortunately not apparent to the naked eye. Some stainless knives are so hard as to be nearly impervious to sharpening. The only way to make sure of what you are buying is to buy it from a store whose expertise you trust.

Another choice is about size. Chef's knives come with blades from 3 inches (really a paring knife) to about 14 inches. There are specialized knife shapes for every kitchen task, but if you are just beginning to build a knife collection, the 8 or 9-inch chef's knife can do everything from slicing a leg of lamb to chopping two cloves of garlic.

As you become more sure of your skill you might eventually want a longer blade. But the most important criterion is how the knife feels to you. Try it out in the store. Imagine that you are chopping a handful of parsley or slicing an onion. The handle should fit your hand comfortably and you should feel in control of the blade. There should be plenty of room for your fingers under the handle as you bring the blade down to chop. Look also at the construction of the knife. To make them sturdier the best knives have full-length tangs, meaning the metal is forged in one continuous piece extending from the blade all the way through the length of the handle. The tang should be riveted securely to the handle with no gaps.

The choice in handles is among wood, plastic and polypropylene. Wood is the least likely to become slippery when wet or greasy, but wood will eventually split or crack. Polypropylene is easier to keep clean and lasts longer, but does become slippery. Plastic and plastic-impregnated wood are the middle ground.

Since a dull knife is practically useless, some means of sharpening it at home is a necessity. Most experts recommend a magnetized steel for this job. The steel has a wooden handle and a shield at the base of the steel to prevent you from sharpening your fingers as well as the knife. The magnetic qualities keep the steel shavings from scatterng all over you and your food. Well cared-for carbon steel knives that have been kept sharp at home need professional sharpening every several years, stainless knives every year. Stainless knives that have been ill-treated will need professional work every six months or so. Most kitchenware stores can sharpen knives for a small charge.

Knives will last longer if they are used with a wooden chopping surface. No knife should be put in the dishwasher, as the high temperature may affect the temper of the steel. The knives are also inclined to rattle around against other utensils, dulling or nicking their edges. Stained carbon steel knives can be cleaned by rubbing a little abrasive cleanser into the blade with a wine bottle cork.