J. G. Kirby saw it all coming. The year was 1921. World War I - the ''Great War'' - was over, and America was ready for a change. The first cars with V-8 engines were on the streets. Pork chops were selling for 37 cents a pound.
Mr. Kirby put those three elements together and came up with . . . the drive-in restaurant.
Kirby and his partner, R. W. Jackson, opened a roadside eatery in Dallas called the Pig Stand. For 15 cents, a patron could sit in his Model-A Ford and eat a ''Pig Sandwich'' made from barbecued fresh ham and served by someone called a carhop.
This was the nation's first taste of curb service, and it was soon sweeping the country like wildfire.
By the 1930s, Los Angeles was being called the drive-in capital of the world. It had a proliferation of oddball eateries shaped like sombreros, ziggurats, and even a piglet through whose six-foot-long snout hot dogs were served.
By the middle of World War II some 70,000 drive-in restaurants dotted the national landscape, their neon signs flashing names like ''Paul's,'' ''Carl's,'' and ''Tiny's'' into the night. Life magazine even put a carhop on its cover.
A decade later, however, the boom was going bust. It had spawned such progeny as the drive-in theater, drive-in banks, drive-in film-processing booths, drive-in auto insurance claims offices, drive-through fast-food franchises, even a drive-in church. But the drive-in restaurant was largely forgotten.
That is, until now.
With historians in the lead and the French fry-munching general public trailing along behind, a wave of nostalgia for the Auto Age is upon us.
Books about diners and drive-ins are being written. Societies for the preservation of roadside artifacts are springing up. CBS's Charles Kuralt devoted an ''On the Road'' segment to roadside restaurants. Someone even filmed a documentary on the Pig Stands.
''What's historic isn't just 'colonial,' '' says Chester Liebs, a professor of history at the University of Vermont and founder of the Society for Commercial Archaeology. He is writing a book on the history of American roadside architecture.
''Bungalows, factories, restaurants - all buildings make up a library of our history,'' Dr. Liebs says. ''And structures built for autos are extremely important.
''Drive-ins absorbed postwar restlessness. They were novel. They broke the monotony of suburbia.''
But perhaps most important, he says, the drive-in gave renewed purpose to ''the second most expensive item a family could buy. The car became a dining room.'' It was a kind of two-for-the-price-of-one opportunity that appealed to American pragmatism and the ever-present desire to be on the move.
''People conducted themselves differently then,'' says B. J. Kirby, son of J.G. Kirby, founder of the Pig Stand. The younger Kirby worked as a carhop at Pig Stand No. 4 in Dallas.
''Carhops started as men, but then, during the war, women became the hops,'' he recalls. ''We worked long hours, split shifts - noon and night. We wore paper caps and white aprons and served the Pig Sandwich.''
Today fresh ham is prohibitively expensive to serve in fast-food restaurants, but 16 Pig Stands, complete with carhops, remain (although Mr. Kirby has turned Pig Stand No. 4 into a steakhouse).
''It's pretty warm down here in Texas,'' Kirby says. ''People probably don't like sitting in their hot cars anymore. But back then, eating in the car was the thing to do. Pig Stands had it all sewed up.''
''During the war, a lot of these places were open all night for the swing shift,'' explains Jim Heiman, a Los Angeles-based illustrator who is writing a book on the history of the drive-in restaurant. ''My parents both worked at a defense plant and would go over about 3 in the morning and have chicken at a place. It's no longer there, of course.''
One of Mr. Heiman's biggest laments about his study of drive-in legacy is the lack of concrete still standing.
''L.A. is such a 20th-century city,'' he says. ''Everything just gets torn down every 10 or 15 years and something else gets put up. People on the East Coast are much more aware of architectural heritage and preservation. It's really rough out here. They even ripped down the Brown Derby.''
So Heiman, who has already written one book on unusual California roadside architecture, has turned to flea markets, or ''swap meets,'' for his historical research. He now has a fat folder of old menus, matchbook covers, post cards, and French-fry holders. He will not lend out anything.
''Most of these I got from one guy who happened to be cleaning out his garage. It was a real fluke that I happened to be there,'' he explains, flipping through the plastic pages of the folder. ''I haven't seen anything this good since.''
We read from some of the menus:
* ''Spaghetti. Genuine Italian Sauce. Hot french roll. Imported cheese or chili. 25.''
* ''Maple walnut sundae. Try it. It's really delicious - 25.''
* ''Hot Chocolate. Made with Milk - 10.''
* ''Appetite Toner. Cole Slaw - 15.''
* ''Hot Turkey Sandwich. It's Roasted - $1.50.''
All the entries seem friendly and inviting. Just what one might have been looking for after a long night on the swing shift.
There's one early caveat emptor: ''Prices subject to change without notice.'' But it seems like a slim threat when everything on the menu is less than $3.
Heiman turns to a menu from the Rite Spot, a roadside restaurant on old Route 66 between Pasadena and Eagle Rock, Calif. ''That,'' he proclaims, ''is where the cheeseburger was invented. A guy put a piece of cheese on a hamburger and people started flocking for miles. Unfortunately, it wasn't a drive-in.''
Hard facts about drive-ins, however, are hard to come by. The federal government does not keep statistics for drive-in and nondrive-in eateries; they are only described as ''refreshment places.''
Myths abound. For instance, there is some discrepancy about the origins of the car window tray. Before the invention of this device, drive-in customers ate off long planks - sometimes padded - that stretched through their cars from door to door.
B. J. Kirby maintains that it was his father who invented the window tray: ''My Daddy designed it in the early '20s, and I have one of the originals on display in my office.'' But other sources claim the car window tray may have originated at the Tam O'Shanter, one of the original Los Angeles drive-ins, which is still operating as a restaurant of ''fine food.''
No one really knows how many drive-ins remain. Most fast-food restaurants now use the more economical drive-through option.
''The drive-in really declined during the '50s,'' Heiman says. ''They went from being a nice, family-type restaurant to being a hangout for gangs. People started to 'cruise' and teen-agers would usually buy one Coke and then stay for four hours.''
Liebs suggests that with changing economic times during the late '50s and '60 s, many drive-in owners simply tore down their establishments and put up fast-food franchises in their places.
Some, however, have chosen to hang on to their carhops, including such widely known establishments as Steak 'n' Shake and A&W.
''Well,'' huffs one official of the Oklahoma-based Sonic Drive-in Restaurants , ''it would be a little hard to get the food to people if we didn't have carhops.''
And then there are the one-of-a-kind drive-ins like Angelo's in Anaheim, Calif., and the Varsity Drive-In in Atlanta that continue to flourish - primarily because they are an anomaly. Angelo's puts its carhops on roller skates. The Varsity bills itself as ''the world's largest drive-in.''
''We have a double-decker parking lot and we serve 17,000 (people) a day,'' boasts Varsity owner Nancy Sims. ''And for football games, we do more than that.''
Mrs. Sims' father, Gordy, opened the Varsity in 1928 at the edge of the Georgia Tech campus to give students ''a cheap place to eat and cash checks.'' It has had the same menu for 35 years.
Although the Varsity still stands by its carhop service, Mrs. Sims confesses that television sets were installed in its cavernous interior to lure the lunchtime crowd with soap operas as well as chili dogs.
''It's a real mix of clientele,'' she says. ''But we've got people eating here today that came when Daddy first opened.''
Angelo's owner, Tony Strammiello, is a relatively new kid on the block. His restaurant started in 1975, and he put in carhops only two years ago.
''Things have gotten so animated and food so bland,'' he says. ''Lots of people like to reminisce. Back then, in the heyday, there were good times - less pressure, more innocence.''
Mr. Strammiello won't say how much business he does, but he claims ''we serve people in the thousands.'' And on the first Friday of every month the place is jammed with people who arrive in antique cars, hot rods, and even Rolls-Royces. Angelo's serves cherry Cokes and holds hula-hoop contests.
''It's a real '50s atmosphere,'' Strammiello says. So successful is this concept that he is actually beginning to franchise.
''I think,'' he says, ''there is just something that people like about a drive-in.''