Restaurant food in New Orleans is not just Creole and Cajun

''To me, Louisiana has the only true American cuisine in the country,'' says Roy Guste Jr., fifth-generation owner of Antoine's Restaurant. ''It's something we've been living with our whole lives, and it is a true generic American cuisine.''

Mr. Guste defined the special kind of cooking native to his area at the Symposium of American Cuisine here last year. He explained the two distinct ways of cooking called country Cajun and city Creole, as well as a third kind of cooking that he calls ''Haute Creole.''

''The Cajun cuisine is the result basically of the French cuisine that came from France through Canada down into Louisiana,'' he says.

''Creole is a more sophisticated, highly developed cuisine,'' he continues. ''This is not to say it is better or worse, simply that it started as a more highly developed cuisine and became something different.

''But the kind of food we serve at Antoine's I like to call 'Haute Creole.' This is a way we have of cooking in New Orleans that developed in the restaurants and exists in the restaurants.''

The New Orleans restaurant style of cooking is the theme of Mr. Guste's second cookbook, ''The Restaurants of New Orleans,'' with photographs by Glade Bilby II (W. W. Norton, $19.95). He is also the author of ''Antoine's Restaurant'' (Carbury-Guste Publishers, New Orleans, $14.95).

Recipes in the new book are from restaurants that typify this kind of cooking , mostly family-owned but not ethnic restaurants.

''There are many super restaurants in New Orleans that are not included in the book, but it's not meant to be a critical guide,'' says Mr. Guste, who learned French cooking in France before returning to operate Antoine's. ''It is simply a guide of the old New Orleans-style restaurant - and some not so old.''

Included in the book are famous restaurants such as Arnaud's, Galatoire's, Brennan's, Broussard's, Begay's, Christian's, Corinne Dunbar's, the Court of Two Sisters, and the Caribbean Room at the Pontchartrain Hotel.

An exception, perhaps, is Chez Helene, one of the truly black restaurants, as opposed to Creole restaurants. Here Leslie Austin does all the cooking in a very small place.

''Antoine's has been around a long time because the New Orleans people have supported it,'' Roy Guste says.

The restaurant is famous for Oysters Rockefeller, but this recipe is not in the new cookbook.

Many food experts have unsuccessfully tried to analyze or copy Oysters Rockefeller, but it remains a secret, which is all part of the magic that exists in this famous landmark New Orleans restaurant.