POTS ARE called by many names, often depending on the country or region in which they are made or the use to which they are put. Often the pot and the characteristic dish cooked in it are developed together and they share a name: thus, terrine, marmite and casserole.

A casserole is a covered pot of earthenware or metal with two short handles or no handle at all. It is meant for use both on a stove top burner and in an oven. In France, a casserole is a "saucepan," but in English, it has come to mean a pot without a long handle.

Well designed casseroles are rather long and wide. The handles will be big enough to give a firm grip but small enought to conserve valuable oven space. Casseroles are not moved about a great deal during the cooling process. Normally, they are filled with ingredients, set in the oven or on the range and left undistrubed until just before the cooking is completed.

The heat in casserole cooking totally surrounds food, the kind of all-enveloping heat that is associated with an oven. It should come at the food from all directions at once and be transmitted evenly through the bottom, sides and top of the cooking vessel. For this reason it is best to select a casserole with the same material on all surfaces and not one which has one metal on the base and another on the sides. The different material results in uneven heat.

Casseroles can be made of earthenware, porcelain, enameled steel, lined copper, anodized aluminum and cast iron. Whichever material you choose, make sure the salls are thick, and therefore able to hold and diffuse heat through many hours of cooking. Be particularly careful to select a casserole with a tight fitting cover. The fit between the pot and the lid should be one through which evaporating steam cannot escape. Casserole recipes call for long slow cooking, cooking in which moisture inside the vessel blends flavors, softens textures and creates sauces. Moist heat is essential to the success of a casserole dish. A slight dome shape to the lid will help with the internal formation of liquid by catching the condensing steam and sending it back to baste the foods. It is the liquid in the casserole that transmits and evenly amplifies the surrounding heat.

There are five excellent brands of casseroles available in the United States:

The Commercial Aluminum Company of Toledo, Ohio, makes a series of casseroles in Calphalon. Calphalon is a dark gray anodized aluminum that will not stain or pit and does not interact with foods. The casseroles are highly heat conductive and attractive. Their lids flip over to become saute pans, an extra value for their rather high price. They come in 2-, 3-, 5-and 7-quart shallow designs as well ad deeper 2 1/2-, 5-, 8 1/2- and 15-quart models. They range in price from $66 to $132.

Magnalite Professional Cookware produced by General Housewares Corporation is also made from dark gray anodized aluminum with attractive lids that fit so well they can be used for waterless cooking. These are also ideal casseroles. They are available in 3-and 5-quart models at $45 and $50 respectively.

Copco has a series of enameled cast-iron pots in various bright colors. The gently sloping, well-balanced shape is a classic example of excellent Danish design. The bottoms have not been coated with enamel which improves their already high heat conductive properties. They are available in 1 1/2-to 7-quart sizes and retail at $32 to $74.

Other attractive and functional casseroles are made by Le Creuset. Le Creuset casseroles are also made from enameled cast-iron. There is a spectular range of colors and sizes. The bottoms have been glazed and fired only once which helps it resist chipping and increases its conductivity over fully glazed and fired bases. They are available in 2-to 13-quart sizes and retail at $29.95 to $99.95.

The great-grandmother of casseroles in America is the Wagnerware cast-iron kettle. This type of pot has been manufactured in the United States for over 200 years. They hung from hooks above burning logs in colonial fireplaces. These pots are extraordinairly heavy, highly heat conductive and very inexpensive. The 5-quart pot with its heat-resistant see-through glass lid and wire loop handle retails for $15.50.