COME HERE in midsummer and you'll understand why New Orleans isn't a great reading or writing town. It's too hot. Everything droops with humidity and fatigue. Canal Street, whose sidewalks are being ripped up and spruced up for the World's Fair next spring, bakes in the heat. The best relief is a Myers's rum and soda at Galatoire's or a streetcar ride up St. Charles Avenue--the big windows slide all the way down and you get a delicious breeze--to Audubon Park and the Camellia Grill, where you may run across Walker Percy sitting at the counter and eating a chili omelette.

The names of famous writers have long been linked with New Orleans, but the fact is that few of them lived here very long. Orleanians like to show off the homes of Tennessee Williams, Truman Capote, and F. Scott Fitzgerald--none of whom did much more than flutter in and out of the city, getting color and sustenance but not staying.

The same is true of Percy, who lives across Lake Pontchartrain in Covington, where the air is clearer and the vegetation dominated by southern pines and not jungle creepers, and of Ellen Gilchrist, who wrote a sensational book of short stories called In the Land of Dreamy Dreams two years ago and a novel, Annunciation, this year. Gilchrist is mainly found in Arkansas these days.

New Orleans is a city constantly poised between the disaster and the big deal--the giant project or scheme that will bring instant success. This year's disaster was a flood (last year's was a plane crash). And this year's big deal is the World's Fair, which actually runs from May to November 1984. "Everybody has some kind of scam," says one New Orleans author. "They're turning houses into hotels with little tiny rooms. They're sticking beds in the closets."

The fair has been the force behind a number of fine publishing projects. Louisiana State Universtity Press, headquartered an hour and a half up the highway in Baton Rouge, is bringing out New Orleans: Yesterday and Today, a collection of anecdotes and history by four famous local newspapermen--Walter Cowan, Pie Dufour, John Chase, and John Wilds--and a marketing consultant named O.K. LeBlanc, a delightful raconteur who used to labor in the service of the local power company.

Also just in time for the fair will be Up From the Cradle of Jazz: A Cultural Portrait of New Orleans, 1949-82, which concentrates on postwar music, a subject that's been largely ignored in a city that dwells obsessively on the past. Its authors are Jason Berry, Jonathan Foose, and Tad Jones.

LSU is the dominant publisher in the state, and it's become one of the most important university presses in the country. Next year's list will include 60 to 65 new titles--double the number in 1975. At least four of those titles will be fiction, an area that LSU has embraced warmly since the success of A Confederacy of Dunces, written by a young suicide, discovered by Percy, and published in 1980. There are now 50,000 hardcover and 500,000 paperback copies of John Kennedy Toole's hilarious novel in print.

Toole's first novel, Neon Bible, which was written when he was 16 has been the subject of much speculation over the past few years. LSU definitely will not publish it, reportedly because of possible legal problems (it seems to be owned by five heirs who can't agree among themselves) and because it's not as rich and mature as A Confederacy of Dunces. Rhoda Faust, the owner of The Maple Street Bookstore, near Tulane, is determined to publish Neon Bible herself, if she can get the cooperation of Thelma Toole, the strong-willed mother of the late John Kennedy.

LSU is very high on another fiction writer these days. He's Lewis Nordan, who, like so many other fine novelists, comes from Mississippi. Nordan's collection of short stories, out this fall, is called Welcome to the Arrow-Catcher Fair. It has an eerie, mad feel to it--a grotesquerie that's almost Orleanian in tone.

This grotesque esthetic, with a nice touch of humor thrown in, seems to be expressed best in photographs and drawings. And two books, both self-published, that will be out in time for the fair, capture the esthetic perfectly. One is Geophysic Wonders of New Orleans, which comprises photographs by D. Eric Bookhardt and text by an eccentric local genius named Jon Newlin. Actually, the new book is a more commercial version of a cult item (of the same name) that appeared in 1975 and quickly sold 2,000 copies.

Bookhardt photographs the great New Orleans necropolis--vast above-ground cemeteries with elaborate monuments that have an Egyptian cast to them--as well as mossy City Park melting in the sun, and the fantastic tribal culture of the Mardi Gras Indians (blacks who dress up in elaborate feathered costumes during the annual Carnival).

The second book is a collection of drawings by Bunny Matthews, whose work appears in the Sunday magazine of the Times-Picayune in a cartoon series. It's called Vic and Nat'ly after its protagonists, who own a Ninth Ward bar and talk in that unique New Orleans dialectic that's a combination of Brooklynese, black English, and pidgin French. Matthews' first book of cartoons, called F'Sure, also self-published and also drenched in local color, continues to sell well in New Orleans bookstores. It's been through six printings. The new one will be called simply Vic and Nat'ly, and Matthews says he's busy turning it into a play, with music.

Bookhardt, Newlin, and Matthews all got their start by working for local alternative weekly newspapers. So did Ellen Gilchrist, whose two works of fiction have been the talk of the town for the last two years. The main preoccupation, especially in uptown New Orleans, where parts of both In the Land of Dreamy Dreams and Annunciation are set, is figuringgout which fictional character is which real Orleanian.

New Orleans bookstores have had a rough time lately. One, near the river uptown, has been turned into a gourmet butcher shop. Two others in the French Quarter have closed. The best ones that remain are Faust's Maple Street (which has a branch on Prytania, the street where Lillian Hellman grew up) and George DeVille's eponymous shop on Carondelet just off Canal; you board the streetcar outside his door.

DeVille is an intense elfin man whose shop is a salon as well as a place that sells books. Upstairs, he has a superb collection of jazz records, and there's usually an art show in progress in the back. DeVille, who has also opened a branch (in One Shell Square, an ugly megalith on Poydras Street), reports that besides Percy and Gilchrist and Matthews, he's selling a lot of copies of The Restaurants of New Orleans by Roy F. Guste, owner of Antoine's, Clasped Hands: Symbolism in New Orleans Cemeteries by the historian Leonard V. Huber, and Red and Hot: The Fate of Jazz in the Soviet Union by S. Frederick Starr, the new president of Oberlin College. Starr has been scholar-in-residence at the Historic New Orleans Collection.

New Orleans continues to be an treasure house for second-hand books. The resourceful Faust, whose mother started the shop on Maple Street 20 years ago, is adding secondhand and rare books to her children's bookstore, next door to her main shop. The expansion will be ready for Christmas.

But right now, it's too hot to think about Christmas or selling books or even reading them. "The old-fashioned steel girders of the Huey P. Long Bridge hung languidly in the most air," wrote Gilchrist in In the Land of Dreamy Dreams. "The sun beat down on the river." And I'm going to Galatoire's for a Myers's rum and punch. Wake me when the World's Fair starts.