St. PATRICK, according to a notoriously truth-bending old friend, arrived in Ireland a long time ago as a missionary. The first thing he did was drive every serpent off the island into the sea, and then he sat down and invented Irish Coffee. So grateful were the Irish for both deeds, they made Patrick their patron saint.

A more reliable source says Irish Coffee was invented at Shannon Airport. Still another swears that Herb Caen, the clever San Francisco columnist whose very livelihood rides on being reliable, reported that Irish Coffee was invented at the Buena Vista bar near the cable car turnaround at Fisherman's Wharf.

"Frankly, my dear, I don't give a damn where Irish Coffee was invented, or by whom; let's just go out and sample some," said the Southernest belle I know.

So, on a recent, lazy afternoon we went transcontinental on the telephone wires -- out to San Francisco, over to Chicago, down to New Orleans, up to New York City and on to Boston -- searching for the perfect Irish Coffee.

With six difference recipes from six respected establishments, a weeklong program of sampling and comparing began. Eight, "palates" were involved, on and off; and, as far as can be determined, all survived.

Originally, a shamrock grading system was planned for rating the recipes -- six for excellent, one for crummy -- but after the very first, full six-fisted round it became obvious that such a plan was unworkable: All the recipes deserve six shamrocks, and all are different, as deliciously different as Chicago and New York City and New Olreans and Boston and San Francisco are as cities.

There are, in the blending of the superlative Irish Coffee, a few prerequisites: What seems to work well is a simple six-ounce wine glass; it's got a nice shape, and the six-ounce capacity is just right. Before pouring any ingredients into the glass, fill it with hot tap water and let it stand a couple of minutes. Pour out the water and begin. This procedure helps things get started and insures the hot coffee will not crack the glass.

Most importantly, make your own freshly whipped cream. Nothing else will do. A little bit of sugar and vanilla can be added to the cream before whipping; it's a sensuous touch.

We begin with the picturesque Buena Vista, located at 2765 Hyde St. in San Francisco. Farmers Brothers coffee (substitute your favorite standard blend or moca java) 3 lumps sugar 1 ounce Buena Vista or Tullamore Dew Irish Whiskey Freshly whipped cream

Fill a pre-warmed 6-ounce bell-shaped fizz glass 2/3 full of coffee. Add the sugar and whiskey. Stir, and then top with freshly whipped cream.

COMMENTS: "Charming . . . deceptive . . . smooth . . . not overpowering . . . yep! . . . appealing to even the nondrinker for its delicacy and smoothness . . . great socializer . . . delightful, delicious, delirious . . . perfect balance of ingredients . . . a well-spent buck-and-a-half."

Chicago's famous Pump Room is nestled in the Ambassador East Hotel at 1301 North State Parkway. 1 ounce Irish Mist (a liqueur, not a whiskey) 1/2 ounce heavy sugar water Superior coffee (substitute your favorite standard blend or moca java) Freshly whipped cream

Into a prewarmed tulip-shaped champagne glass pour the Irish Mist.Add the sugar water and fill the glass 3/4 full of coffee.Top with freshly whipped cream.

COMMENTS: "Smooth, that's the word, like a hot cloud . . . fruity . . . more natural taste . . . distinctive . . . almost as if it has Grand Marnier in it . . . not the sort of drink one would like to get bombed on, but a great single hit . . . real nice . . . not harsh . . . delightful! . . . rich, mysterious flavor of spices and honey . . . subtly tasteful.

For Irish Coffee in New Orleans, one goes to Brennan's at 417 Royal St. in the French Quarter. French Market-type coffee with chicory 1 1/2 ounces Jameson Irish Wiskey 1 cube sugar Freshly whipped cream

Fill a prewarmed 6-ounce wine glass 3/4 full of chicory coffee. Stir in the whiskey and sugar and top with freshly whipped cream.

COMMENTS: "Lots of character . . . not for the nondrinker . . . very distinctive and the most different . . . pleasant chicory aftertaste . . . packs a punch . . . smooth . . . dinner party drink for finishers . . . as much character as New Orleans itself . . . excellent Southern charm."

John Barleycorn is a well-known New York City establishment and is located at 209 East 45th St. Cafe Royal (substitute your favorite standard blend or moca java) 1 1/2 ounces Powers or Jameson Irish Whiskey 1 ounce brown sugar Freshly whipped cream

Fill a prewarmed 10-ounce wine glass with 6 ounces of coffee. Add the whiskey and brown sugar. Stir and top with freshly whipped cream.

COMMENTS: "Real good . . . smooth . . . kind of nippy . . . got a fine edge on it . . . goes down well . . . very civil . . . something you drink in a three-piece Pierre Cardin . . . needs another teaspoon of brown sugar."

In Boston it's Daisy Buchanan's, at 240 Newbury St. Sugar Autocrat Coffee (substitute your favorite standard blend or moca java) 1 1/2 ounces Jameson Irish Whiskey Pinch cinnamon Freshly whipped cream Creme de menthe

Dip the rim of a steamy and prewarmed beer mug into a bowl of sugar, thinly coating about 1/2-inche of the inside and outside surface. Add the coffee, whiskey and cinnamon and then top with freshly whipped cream. Sprinkle a little creme de menthe atop the whipped cream.

COMMENTS: "Interesting . . . robust . . . strong . . . easy drinking . . . nice tang and a good Boston twang . . . winter drink . . . one more please."

The Man in the Green Hat is at 301 Massachusetts Ave., Nw, Washington, D.C., and serves Irish Coffee with a kick. 1 ounce Tullamore Dew Irish Whiskey 1/2 ounce Kahulua International coffee (substitute your favorite standard blend or moca java) Freshly whipped cream

Into a pre-warmed 10-ounce stem glass, pour the whiskey and Kahlua. Add 6 ounces of coffee and top with freshly whipped cream.

COMMENTS: "The Kahlua is a pleasant tough . . . makes cold weather worth it . . . not too much of a whiskey taste . . . subtle blend . . . a good compliment to the cream . . . tell the president."