SANTA CLAUS, Ind. (AP) _ The Pizza Parlor, a tiny restaurant smaller than many people's kitchen, is the only slice of Italy in this old German town.

Owner Gerry Durnell says he serves just three or four of the town's 600 residents some days, but that's enough for his purpose.

Many customers probably don't know it, but the little restaurant in their out-of-the-way town is America's pizza think-tank - a sort of secret laboratory for the industry.

Hidden behind the dining room is a cluster of offices from which Durnell directs the National Association of Pizza Operators and publishes Pizza Today magazine, a trade journal distributed every month to 39,000 pizza makers all over America and in 28 other countries.

The pizzeria is there mainly to give him ideas and insight for his trade group and magazine.

''We run it because it keeps us on our toes,'' he said. ''We get the benefit of a lot of first-hand experience being out there on the front line, dealing with customers and selling the product.''

Durnell said he saw the need for a national pizza trade group when he started his restaurant five years ago and found there was no place he could go for help and information.

The pizza operators association now offers special insurance, workers' compensation subsidies and a 24-hour ''pizza hot line.'' The group also puts on Pizza Expo, an annual trade show where its Golden Pizza Award is presented to outstanding pizza makers.

Before getting into the pizza business, Durnell, 43, was an Army pilot, writer, photographer and state representative from Springfield, Mo. He came to southwest Indiana as creative director for Abbey Press, a mail order business operated by the monks of St. Meinrad Archabbey.

He put his media skills to work on creating Pizza Today at the same time he was organizing the trade group.

Before long, those two ventures had grown to the point where his restaurant was just a sideline.

Pizza Today is a slick, full-color production that runs to 70 pages and covers every facet of the business.

Recent articles included ''Seafood Pizza, Mussel in on the Trend,'' ''The Evolution of the Rolling Pin'' and ''Sanitation: Pizza's Most Important Ingredient.''

In each issue, the magazine profiles a ''Pizza Maker of the Month,'' and it recently added a ''Pizza Bytes'' column describing special computer applications for the pizza business.

The magazine is crammed with pizza trivia. Regular readers know, for example, that olives were first cultivated by the Syrians more than 5,000 years ago, that a pound of oregano will season 6,900 slices of pizza, and that the Greek philosopher Plato had his own favorite pizza recipe.

''Everybody asks, 'What can you say about pizza month after month?' Our real problem is not having enough space to say everything we want to,'' Durnell said.

The magazine is the only publication catering exclusively to the pizza business, he said, so it is filled with ads for pepperoni, cheeses, ovens and other supplies.

''It's the easiest way we know of to reach that particular industry, said Chip Schweiger, sales manager for AABeco Corp., a Cleveland-based oven manufacturer.

''We read it rather religiously,'' said Walter Bagot, a vice president at Noble Roman's Pizza Inc., a chain operating 123 restaurants in five states. ''I always find it very helpful in keeping up with the industry.''

Durnell's pizzeria has only six booths and a single oven, but he said its trials and trumphs are those of pizza makers everywhere.

''Everybody has the same types of problems,'' he said. ''Portion control, for example, is just as vital to a small operation as a big one. If something works or doesn't work here, it will probably have the same effect somewhere else.''

Nevertheless, some people are taken aback when they find out his headquarters is in a town they cannot find on most maps.

Located in the hills of southwestern Indiana, Santa Claus was given its unusual name in 1852 at a Christmas Eve meeting of the town's German immigrant settlers.

''People ask me all the time, 'What are you doing there?''' Durnell said.

Most Pizza Today articles are about accounting, advertising, insurance, personnel and other concerns shared by every small business, but tailored to the pizza industry.

''We're always looking for that slant,'' he said.

The magazine's contributors have included some of America's foremost food writers, including Pasquale Bruno Jr. and James Beard.

Durnell and his staff themselves will go to great lengths for an article.

They have been to London, where tuxedoed waiters serve pizza with champagne and live chamber music, and to Los Angeles, where gourmet chefs make pies topped with things like buffalo-milk cheese, duck and squid.

''Any time we're in another city, the first thing we do is look at the yellow pages and see what's going on in pizza,'' he said.

Pizza is the fastest-growing segment of the food industry, he said, and is sold in about 50,000 restaurants.

Durnell wants to publish more magazines eventually, but has no plans to expand his own restaurant.

''It's about as big now as I have time for,'' he said.