Not only is the making of sausage an established German tradition, but the cooking and serving of it has unwavering rules. Here are some that Usinger's considers most important:

* Cold sausages should be sliced thin, particularly since some of them are tough. It is better to serve two or three thin slices than one thick slice. Be sure to peel the casings from cold sausages before they are eaten.

* Summer sausages are among the least perishable of all sausages. They keep best unwrapped; a white salt coating on the casing is characteristic.

* Link sausages--with the exception of fresh pork sausage--are already cooked, and need only warming.

* Never boil any link sausage, or the casing may split, allowing flavorful juices to escape. Put it in water to cover and warm to a simmer. Cover the pot and turn off the heat. Let wieners sit in the hot water 5 to 7 minutes, thicker sausages like knackwurst 10 to 15 minutes. If you let them sit in the water too long, the spices and flavor will dissipate into the water.

* While German potato salad is the ultimate accompaniment, sauerkraut and scalloped potatoes are considered acceptable. "We believe in rye bread," added Siebecker, cautioning that it was to be "eaten on the side." With beer, of course.

* Grilling is "the only way to cook bratwurst," declared Siebecker. So subtle is the taste of bratwurst that it should never be cooked in water. Grill over a fire that has cooled to a gray ash, or the sausages may split from excessive heat. Turn often to brown evenly on all sides, and do not overcook. Or fry in butter over low heat, turning often, with tongs to avoid piercing the casing.

* Plan on two hot sausages per person. Unless you live in Milwaukee.

Here are the sausages to choose from if you live in Washington.

BLOOD SAUSAGE

Made with beef blood and thoroughly precooked in natural casings, they can be served hot or cold. Their shelf life is ten days to two weeks. The following are available in Washington.

Blood Pudding (also called Long Blood Sausage): Smoked and interlaced with bits of cured ham fat. Serve as cold luncheon meat or slice and fry.

Thueringer-Style Blood Sausage: Homemade style, bits of ham fat, pork, liver and onions with a light smoky flavor. Slice and serve cold or fry.

Tongue Blood Sausage: A large slicing sausage made principally of pork tongue which looks like a mosaic. Slice thin and eat as is.

LIVER SAUSAGE

Made of pork and pork livers, to be sliced or spread on bread or toast. Shelf life is about 10 days. The following are available in Washington:

Braunschweiger Liver Sausage: Flavored with bermuda onion and light smoke, made in a natural casing.

Goose Liver Style: A small, lightly smoked liver sausage larded with pork tongue and pistachio nuts.

Hessische Brand Landleberwurst: The original "schmierwurst", heavily smoked and spreadable, with a mellow flavor. Serve as an hors d'oeuvre with crackers.

BRATWURST

Made of finely ground pork and veal, with a pale color and delicate flavor. Should be served hot, grilled over charcoal or browned in the frying pan. Thoroughly precooked. No nitrites. Extremely perishable and should be frozen if not served within a few days of purchase.

KNACKWURST

Blend of pork and beef, lightly flavored with garlic. Precooked; heat in water before serving. Should be kept frozen if not cooked within a few days of purchase.

HEADCHEESE

Finely diced pork seasoned with spices and vinegar, lightly smoked and jellied. Serve cold. Should be frozen if not cooked within a few days of purchase.

GERMAN-STYLE HEADCHEESE (SCHWARTENMAGEN)

Similar in appearance to regular headcheese, but made with larger pieces of pork and no vinegar, more heavily smoked. Serve cold. Should be frozen if not cooked within a few days of purchase.

TEAWURST

Finely chopped meat with heavy smoke flavor. Serve cold as a sandwich spread.

CERVELAT OR SUMMER SAUSAGES

These long-smoked, air-dried sausages keep well because much of the moisture has been removed through the drying process. They keep up to one month, hold up best if left unwrapped and should be served sliced cold. Here are the varieties sold in Washington:

All Beef Summer: Beef, with a heavy smoky flavor.

All Beef Salami: Beef, with a heavy smoky flavor, seasoned with garlic.