SINCE WELL before the Renaissance in Basel, Switzerland, Carnival revelers embarking on a three-day nonstop round of merrymaking have fortified themselves with a special breakfast.

The conservative populace then take to the streets in the most outrageous Fasnacht in Switzerland, and yet it is probably the most cerebral in the Christian world.

In New Orleans, Carnival is celebrated with all-night jazz sessions; in Munich it's an occasion for artists' balls and free-form promiscuity. At what is probably the most famous Mardi Gras of all, Rio de Janiero's, tempestous orgy is the keynote. In Basel, at midnight masques come off, but that's about all that is removed, for in the sobering cold of the Alpine winter, conviviality, not debauchery is the mood.

Fasnacht is the occasion to satirize with wit and irony in sophisticated verse and artwork the foibles and furies of the past year's events and celebrities. Considerable preparation, ingenuity and expense are devoted to costumes that are amusing rather than erotic.

During the reformation, in defiance of the pope, the Baselers began their Carnival on the first Monday after Ash Wednesday, and they still do, even though the rest of the Christian world celebrates it before. Originally it was an all male event. But early in this century women formed their own piccolo and drum groups and have gradually been incorporated into the oldest groups, the Cliquen. There are about 100 of them, each with from 50 to 200 members. Year-round rehearsals of the musicians take place in soundproof cellars which serve as clubrooms.

Each clique selects and keeps secret its theme. Perhaps it's some local scandal or an inept official. The subject is satirized in the choice of official costume the members wear, the floats and most especially in the grotesque masques. Verse as well as art adorns the lanterns, which may be as high as 14 feet and require several of the strongest men to carry.

On Monday morning, March 9th, everyone will be out on the streets of the city. Seconds before 4 a.m., all the lights of the city are extingushed except those inside the giant lanterns. On the hour, the bells of Basel peal, and the fife and drums play the few bars of an old Swiss military march. The entire city echos the same melody, Morganstraech. By the eerie illumination from the huge lanterns, the groups slowly wind their way through the cobbled lanes.

At dawn, only on Monday, it is traditonal to have mehlsuppe, onion and cheese tarts at the pubs, which have opened earlier to cater to the celebrants. Then, it is back to the street to drum -- which is normally forbidden.

At 1 p.m., after having changed into the official costume, all the groups gather at their appointed sites to begin the official parade, which goes on in one form or another -- if you have the stamina -- until dawn on Thursday.

All motor traffic in the city halts between noon and daybreak during Fasnacht to allow uninterruped passage of Zuge, the formal processions. In the lead come the clique's "space maker's," men on horseback, or people on foot who are either not sufficently proficient on instruments or too old to participate in the most strenuous activites. These folks distribute the Zeedel (verse satirizing their theme). Next come the lanterns resplendant with the phantasmagoric figures and the text of the Zeedel. Fifers and drummers, well-rehearsed, precede the floats from which descend on the bystanders golden mimosa and oranges and confetti.

But there are many participants who are not members of an established club. These independents are content to parade with prams, toy wagons -- almost anything on wheels that they can decorate. An undoubtedly, among the throng will be Alte Tante (spinster), who characteristically wears an enormous hat festooned with flowerpots, feathers, veils and miscellanea. Then there are the Waggis (a slang term for the neighboring Alsatian peasants, who are recognized by thier blue blouses, white pants and boisterous behavior.

Let's not forget the Guggemusiken (rag-tag bands) -- it's hardly likely. These groups play pop tunes in utter dissonance. Only one member actually plays the established melody; the rest purposely make mistakes, playing on old wash tubs, pans, saxophones, and to aggravate the well-rehearsed fife and drum corps.

In the evenings, after hours of marching through wind and snow, the hordes of exuberant merrymakers dine in restaurants which advertise Schnitzelbanggler. These are minstrels who perform the original songs satirizing their own "target." Their subject is illustrated in cartoons on broadsides and held aloft on portable easels. This is another opportunity for the unaffiliated Fasnachtler to express himself.

During the holiday all masqued persons in this rather formal society are entitled to address others in the familiar du. But, more important, perhaps the raison d'enetre of the disguise is the opportunity to vent one's true feelings without fear of retribution. If, in the costume, you meet your boss in a pub, you can freely ridicule his idiosyncracies: the preference for red socks, or green bow ties . . . or worse! This is not intended to be a monologue; the object of derision replies in kind. The barbed rejoinder of the dialogue amusement for those within earshot. Well-done, this intrigieren is infectious, and the witty repartee continues all throughout the night.

And so it goes for three days and nights: parades, music, pranks, ridicule, eating and drinking and cacophony. Then finally, before daybreak, those undaunted celebrants who have enough energy gather for a final jam session and breakfast at the train station in the Bahnhof Buffet.

Giant snowplows glean the fields of confetti and, by sunrise, the Swiss sense of order descends upon the city as the streets are cleared of paper. But here and there a hardy reveler is straggling home, costume a bit bedraggled, step a trifle weary, already fantasizing about the possibilites for next year's Fasnacht. BASLER KASEWAHE (Basel Cheese Tart) (6 to 8 servings) 9-inch pie shell, partially cooked, or 1/2 pound puff pastry dough, partially cooked in a 9-inch pan 1 cup gruyere cheese, finely grated 1 cup heavy cream 1 cup milk 4 eggs Salt, pepper, nutmeg to taste 6 tablespoons sweet butter 3 tablespoons flour

Spread the grated cheese evenly over the pre-cooked dough. Mix cream, milk and eggs together in a large bowl. Season with salt, pepper and nutmeg. Melt the butter and add to egg mixture. Very gradually add flour. Pour mixture over cheese. Bake in preheated 325-degree oven for 40 minutes or until knife inserted in center comes out clean. BASLER ZWIEBELWAHE (Basel Onion Tart) (6 to 8 servings) 2 strips bacon, diced 2 cups sliced onions 2 ounces pork fat Salt and pepper to taste 1 teaspoon paprika 1/2 teaspoon sage 9-inch pie shell, partially cooked, or 1/2 pound puff pastry, partially cooked in 9-inch pie pan 1 cup heavy cream 1 cup milk 4 large eggs 2 teaspoons flour

Fry diced bacon slightly. Add onions and pork fat and cook until soft. Do not allow to brown. Season with salt, pepper, paprika and sage. Spread mixture evenly on pie dough. Mix cream, milk, eggs, and flour and pour over onion mixture. Bake for 40 minutes in preheated 325-degree oven. BASLER MEHLSUPPE (Brown Onion/Flour Soup) 1 cup flour 1 cup onions, finely chopped 3 cups pork fat 2 quarts beef broth 2 ounces bacon rind 1 cup dry red wine Salt and pepper to taste

Dash wine vinegar 4 ounces grated parmesan cheese, optional

Brown flour without any fat in a heavy roasting pan. In another pan, simmer onions in pork fat until golden brown and greatly reduced. Add browned flour to onions. Gradually add hot broth, stirring continuously, to flour-onion mixture. Add bacon rind and red wine. Cook on low flame, partially covered, for 4 hours. Skim fat and add salt, pepper and vinegar to taste. Serve with grated cheese.

Recipes courtesy Chef Franz Josef Kuhne, Basel Hilton Hotel