"You should have been here 20 years ago!"

Why are people always saying that? Why do I always get to a place when it's past its prime? If old-timers never told me how wonderful it used to be, I might think wherever I was was absolutely wonderful.

But the you-shoulda-been-here-yesterday theme at New York's 54-year-old San Gennaro Festival, described as the largest religious street festival in the United States, was echoed by several vendors. "It's become more commercial," said one. "It used to be more fun." That may well be, but you can't convince the 3 million people who come every September. The festival's religious aspects tend to get buried in the vats of boiling fat for the calzone and zeppole , in the barkers' cries for the games of chance and in the loudspeaker welcoming a planeload of visitors from Naples, busloads from Canada, Ohio, and upstate New York on behalf of Mayor Koch. The welcoming spiel is often pierced by lost child announcements: "Andy Greenspan, your father is waiting for you at 140 Mulberry Street."

Mulberry Street. The heart of New York's Little Italy. Where Joey Gallo got rubbed out. Where the Italian-American civil rights organization, Joe Colombo's old group, has had a stand for the last 15 years at the San Gennaro Festival. Except that's not what Little Italy is all about. It's a section of New York, just across Canal Street from Chinatown, where there's a plaque on the wall of a building -- "In memory of PFC Frank Vallone, Sept. 11, 1968, USMC"; where old people still sit out on the sidewalk on warm nights in beach chairs and kitchen chairs; where young Italian Americans born and raised in the neighborhood who had moved away are moving back; where old buildings are being restored and new businesses moving in. "It's a very safe neighborhood," says a longtime resident.

The festival has gotten so big it has spilled out of Little Italy across Canal Street to Chinatown where the food is still Italian, but in deference to the location and the Chinese who come to eat and play on that side but won't cross Canal Street to go to the Italian part, many signs are in Chinese. The Italian American band, which plays spritely music but marches at a funereal cadence down the center of Mulberry Street when a celebrity visits (it was the mayor when I was there) has a Chinese trumpet player.

The festival is run by the Society of San Gennaro, a fraternal and religious group of Italian-Americans. Its current president, Arthur Tisi, is the grandson of the founder. Tisi says his grandfather and some other Neopolitans got together in 1925 and invited everyone to Mulberry Street to eat chickens. The festival honors Naples' patron saint, who was beheaded in 350 A.D.

For 11 days a feste 'e tutte 'e feste, "the festival of all festivals" is curb-to-curb people. A lot come to lose, or maybe win, some money at dozens of different gambling stands. But the Neopolitan food is still the primary attraction. They sell 2 million sausage heroes alone, along with dozens of other Italian specialties, which in recent years have been joined by Chinese, Philippine, Mexican and Spanish foods. You don't have to be Italian to rent space for your stand. You certainly don't have to be Italian to enjoy the food, and you don't have to be rich. You can have three zeppole, Italian donuts, right out of the hot fat for 50 cents; stuffed shells or manicotti for $3.50; hot scungilli (squid) with sweet or medium hot sauce for $4; calzone, more fried dough, this time filled with ricotta, mozzarella and ham for $2; stuffed artichokes at $2.50. Two dollars will buy you a rice ball filled with cheese and ham or meat; Italian ices for 75 cents; rich gooey desserts -- cannoli, sfogliatelli, pastagioti and pasta croce, each for 75 cents; pizza, of course. Should you want to break out of the Italian mold you can try antipasto in pita, baklava, shrimp salad nicoise, funnel cakes from Pennsylvania Dutch country, tacos, souvlaki, chocolate-dipped strawberries, egg rolls, bean-sprout fritters, Eileen's cheesecake, pina coladas. Most come with napkins; a few with paper plates and plastic forks. I think I saw some hot dog stands, too, but after I tried every food that I've listed with its price, there wasn't much interest in hot dogs.

The food is not that of a top-quality Italian restaurant. And it is uneven. Some stands have better zeppoles, better Italian ices, better pastries. Either you know from having tried them all over the years or you ask. People are happy to share their advice. As I was purchasing the pastries at one stand, a lady leaned over and said: "Buy them inside. They're cheaper. Only 75 cents."

"Yeh. She's right," chimed in another complete stranger.

But you don't go to the San Gennaro Festival because you are looking for bargains or because you expect to find the ne plus ultra of Italian cooking. You go because you've heard about it for years, because nowhere but in New York could you have such an experience and because even a lousy sausage-and-pepper hero tastes good on a late summer afternoon when the sun is shining and everyone is smiling.

Next year, maybe it won't be quite as good as this year, but around the 11th of September, if you are in New York . . . NEAPOLITAN TURNOVERS (Calzoni) (12 turnovers) 1/2 recipe for pizza dough, (see recipe) 1/4 pound prosciutto or ham 1/4 pound mozzarella cheese, thinly sliced Olive or salad oil Salt, pepper

Place the kneaded ball of dough in a large bowl. Cover with a tea towel. Let rise for 2 hours, until doubled in bulk. Roll it out on a floured surface until very thin. Cut into 3-inch rounds. On half of each round place a piece of prosciutto and a slice of cheese; sprinkle with oil, salt, and pepper. Fold over into a half-circle. Pinch the edges firmly to enclose the filling. Bake at 425 degrees for 15 minutes, or deep-fat fry in hot oil until golden brown. Serve as a snack with drinks. PIZZA DOUGH (Pasta per pizza) 1 package dry or compressed yeast 1 teaspoon salt 2 tablespoons olive or salad oil 4 cups sifted flour

Dissolve dry yeast in 1 cup very hot water or compressed yeast in 1 cup lukewarm water; add salt and let stand for 3 minutes, then stir until dissolved. Pour 2 tablespoons oil into a bowl; add yeast mixture, then half of flour and beat smooth. Gradually stir in remaining flour. If necessary, add a little more water to make a smooth soft dough. Knead for 4 minutes. Adapted from "The Gold Medal Italian Cookbook" by Marie Roberson Hamm SFOGLIATA DI MELE (Apple Flaky Pastry Turnover) 1 recipe pasta sfoglia (see recipe) Filling: 2 1/2 pounds apples 3 tablespoons butter 1/4 cup granulated sugar 1 teaspoon vanilla extract 2 tablespoons cognac 1 egg 1 tablespoon powdered sugar

Roll out pasta sfoglia, rounding edges, to a 1/2-inch thickness. Place on baking sheet.

Wash and peel apples and cut in thin slices. Place in a saucepan with butter and cook at medium heat until soft. Put into bowl; sprinkle with granulated sugar, vanilla, and cognac and set aside. When cool, place on half of pastry and fold other half over. Close well by pinching edges. Brush pastry with slightly beaten egg. Bake at 325 degrees for about 1/2 hour. Five minutes before removing from oven, sprinkle sfogliata with powdered sugar. Serve cold. PASTA SFOGLIA (Flaky Pastry) 2 cups flour Pinch of salt 1 egg (optional) Ice water 1 cup butter

Sift 1 1/2 cups of the flour with the salt on pastry board. Make a well in center, add egg, and mix, adding enough ice water to make a rather consistent dough. Knead for a few minutes, then chill half an hour. Mix together remaining flour and butter separately. Wrap in foil and chill.

Roll out the first dough mixture into a rectangular sheet. Then roll out butter-flour mixture into another rectangle; it should be almost as wide as the first dough, but only two-thirds as long. Place the butter-flour rectangle on top of the dough in such a way that a "flap" of dough is left uncovered at one end. Fold this flap over the butter mixture, then bring the other end of the dough up to cover the flap. The dough should now resemble a letter that has been folded. Turn the dough so that the short end is facing you, and roll it out again. Fold it three times, like a letter, as before.

Chill 30 minutes. Repeat procedure two more times until dough is ready to be used. Adapted from "La Dolce Cucina,"by Anna Bruni Seldis.