The high point, they say, was on a summer day in 1883 when a cowboy named Teddy Blue Abbott, looking for strays on a cattle drive, came over a rise near the North Platte and saw seven herds behind his own, eight more in front and in the distance, as far as he could see, towers of dust raised by 13 other herds.

"It looked, he said, as if all the cattle in the world were coming up from Texas."

The words belong to Lonn Taylor, who is guest curator of a magnificent new show at the Library of Congress: "The American Cowboy."

Filling a two-story gallery at the Madison Building, the giant exhibition opening Saturday will remain here until Oct. 2 and then will move to San Antonio; Denver; Calgary, Alberta; and San Jose.

It has old photos, Frederic Remington paintings and sculptures, spurs and saddles and Will Rogers' lariat and a real chuck wagon with coffee-cup rings still staining the worn boards.

It has movie posters; a video talk by flint-eyed William S. Hart, the Old Man of the Westerns; recorded songs; a '50s Naugahyde drugstore booth with juke box feeder; cowboy commercials from turn-of-the-century Cream of Wheat ads (painted by N.C. Wyeth, no less) to the Marlboro Man and a Ralph Lauren cologne called Chaps; films of modern ranching with helicopter and pickup; manuscript pages from "The Virginian"; and Buffalo Bill and Tom Mix and John Wayne and Roy Rogers and--sporting a beer belly you would never see on his precursors--a statue of a cowboy, done with chainsaw and house paints by Lionel Adams in 1979.

It is a rollicking show, and a serious study of a great American myth, and shining through it all is unabashed love. Taylor, from the Museum of New Mexico in Santa Fe, led a mesmerized crowd through the exhibition at the press showing yesterday. Some of his fascinating lore appears in his essay for the 228-page catalogue, which soon will appear in hardback.

From a caption of an early cowboy photo: "His rather elaborate equipment includes a rubberized slicker, field glasses and saddlebags, and his method of holding the reins indicates that he learned to ride in the East or in England," for the breed was "a mixture of old hands who had come up from Texas, eastern college graduates working for the experience, British remittance men and midwestern farm boys."

The show covers five phases: the original riders of the open range; the romantics, inspired by Remington, Theodore Roosevelt and novelist Owen Wister; the entertainers, from Buffalo Bill on into the movie heroes; the mythic figures of ads and TV commercials, curiously promoting a world of purchased leisure that the hard-working cowpokes never knew; and--"meanwhile, back at the ranch"--the modern reality.

There is plenty of nostalgia here for almost any age: a Tom Mix decoder badge from the '30s (you sent in a dime and a Ralston box top), a Lone Ranger pedometer, a tin-can telephone, a badge that howled like a siren when you blew on it. There is a gaggle of Roy Rogers artifacts, John Wayne and Gary Cooper pictures, rodeo scenes.

But surely it is the early reality of cowboy life that will stop most viewers in their tracks. There are no gunslingers here, just hard-working men--a third of them black or Mexican, belying the all-white Hollywood image. A series of great photos by Erwin E. Smith, circa 1910, catches the authentic look of those men, lean and hard-bellied in their denim shirts, already beginning to imitate their own legend with the rakish hats and the dangling hand-rolled cigarettes. And the trail life, the dust and mesquite, the unnumbered cowpaths through the endless prairie, the cowhands in their chaps roping and branding heifers, the chow-down around the chuck wagon, the bedrolls and bean buckets, the sweaty adventure of it all: No wonder we yearn for those lost days.

A moment captured: A cow pony has just stepped in a gopher hole, throwing his rider. The other cowboys rein in, wheel their horses, rush to help the fallen man.

"Ten years of hard riding was about all the human body could take," Taylor writes. He quotes an old-timer: " 'Some of my experiences were going hungry, getting wet and cold, riding sore-backed horses, going to sleep on herd and losing cattle, getting cussed by the boss, scouting for graybacks (lice), trying the sick racket now and then to get a night's sleep . . . but all of these things were forgotten when we delivered the herd and started back to grand old Texas . . . I always had the "big time" when I arrived in San Antonio rigged out with a pair of high-heeled boots and striped pants and about $6.30 worth of other clothes. This "big time" would last but a few days, however, for I would soon be busted and have to borrow money to get out to the ranch . . .' "

An 1875 map issued by the Kansas Pacific Railway shows the trails working up from the Gulf through Texas and Indian Territory, converging into the Chisholm Trail to Ellsworth, Kan., where the cattle were put on trains to Kansas City. As farmers settled near the railroad, the drives had to move farther west to Dodge City (still Fort Dodge on the map).

What is most surprising is how brief this fabled era was. It started after the Civil War, with the development of the railroads and the invention of meat refrigeration techniques. (The transcontinental railroad of 1867 also spawned the myth when it brought eastern journalists like Ned Buntline into contact with the colorful cowboys.) The era of the open-range system by which cattle transported themselves to the boxcars ended abruptly in the terrible winter of 1886, when overstocking and record snows killed 3 million longhorns, dropped the bottom out of the market and forced total reorganization of the business. The new barbed wire enabled ranchers to fence their cattle and feed them cultivated food.

"Wells and windmills began to appear," Taylor writes. "Homesteaders began to take up much of the open range . . . By the nineties, cowboys dug postholes, fixed fences, repaired windmills and drove mowers and hay balers."

It was all over. Frederic Remington: "I knew the railroad was coming. I saw the men already swarming into the land. I knew the derby hat, the smoking chimney, the cord-binder, and the 30-day note were upon us in restless surge. I knew the wild riders and the vacant land were about to vanish forever."

Still, when you cut through the fantasies of cowboy life that followed and get to the final stage of this wonderful show, the romance is still alive in the American West. Spend some time with the video scenes of life at the 96 Ranch: the slow talk, the leathery faces, the trusty pickup ("the pickup truck and veterinary medicine changed everything," Taylor says), the steamy breath of horses being saddled at dawn . . . the beauty is still there, if you look for it.