The Hopeful Stakes, which will be run for the 77th time Saturday, has traditionally been a showcase for elite 2-year-old thoroughbreds. Secretariat scored the first major stakes victory of his career in the race; so did Man o' War, Native Dancer, Affirmed and a long roster of champions.

This year's Hopeful might be a memorable one, too, when a brilliantly fast, unbeaten, New Jersey-based colt, Out of Hock, tries to prove himself against top-class opposition. But he, or any of the great horses who have won this race, could ever match the drama of l973. Rarely in the history of the sport has such an improbable horse scored such a storybook victory.

Not long before his Hopeful triumph, Gusty O'Shay had been soundly beaten in a $5,000 maiden claiming race at Charles Town; he would finish his career in low-level claiming races, too. Only a couple of years before he brought Gusty O'Shay to Saratoga, trainer Harrison Johnson had been driving a bus for the D.C. Transit Co. Now he is training an undistinguished group of horses stabled at Bowie.

But on one August Saturday in 1973, the heavens were smiling on the man and the horse, and Johnson still remembers it vividly. He recalled that he had been training horses for about two years for Mr. and Mrs. Tyson Hopkins, owners of a small farm in Great Falls, Va., when they sent him a gelding by the obscure stallion Rose Argent out of a $2,500 mare named Stormy O'Shay. Even if Johnson had been experienced enough to tell a good horse when he saw one, he would have had no reason to suspect at first that Gusty O'Shay was anything special.

After losing at Charles Town, Gusty O'Shay went to Delaware, where he won a $7,500 claiming race, then stepped up to $15,000 and won by six. "I kind of realized that he was a good horse when he won for $15,000," Johnson said. "At that time, that didn't seem so cheap. There was no good race around to run him in so we decided to take him to Saratoga."

Johnson hooked up a horse van to his car and drove Gusty O'Shay north to run in the Saratoga Special, a stake during the first week of the meeting. When the gelding finished second, Johnson decided to come back for the Hopeful.

"It didn't seem like a big deal to me," Johnson said, but any outside observer might have appreciated the extraordinary scene in the Saratoga paddock before the Hopeful. Under one of the elm trees, the Ogden Phipps clan, the patriach of the American turf, had gathered to watch their regally bred colt Take By Storm being saddled. And right next to Phippses was Harrison Johnson, a black man who got interested in racing while his father worked as a domestic for a prominent Virginia breeder.

He had picked the optimal time to be in Saratoga with an ill-bred speedball. The field was one of the worst ever assembled for the Hopeful. And the track had as strong a bias as a track can have; there was such a hard, fast path on the inside part of the track that every race was won by a front-runner who got to the rail.

Gusty O'Shay broke from a favorable post, dashed to the rail, disposed of the other speed horses and then held on to win by half a length over Take By Storm. In the directors' room after the race, members of America's breeding establishment were drinking champagne toasts to a son of Rose Argent. Members of the press, accustomed to interviewing titans of industry after these big races, asked Tyson Hopkins about his business background. "I was in the sewers for 20 years," he said. "I built a tunnel under Rock Creek Park." Mrs. Hopkins was spectaculating about the next year's Kentucky Derby.

Of course, none among Gusty O'Shay, Johnson or the Hopkinses ever got anywhere near Churchill Downs. When the gelding ran again on a more normal track against legitimate opposition, he was trounced. After that, Johnson said, "He came up with tendon problems; he bowed and rebowed a couple of times."

Gusty O'Shay kept running until he was 7 years old, and wound up in $11,500 claiming races. Eventually, the owners gave him away to people who wanted him as a riding horse, but Gusty injured himself again and had to be destroyed.