Wild hooves thunder on the sand. Nostrils flairing, an untamed Arabian stallion rears and gallops away. Then, slowly, the big black horse turns around and walks gingerly toward a small outstretched hand offering seaweed. The hand belongs to a boy named Alec Ramsay, and the horse is about to become his horse, The Black Stallion, star of a whole series of books, of a hit movie and of the Washington International Horse Show, which opens Sunday at the Capital Centre.

Exciting as the fictional saga of the horse and his boy is -- the shipwreck, the fire, the exhausting swim to safety and the neck-and-neck run for the finish line -- there are two real-life horse stories that star the same horse.

One is the story of a girl and her first show horse, of a tragic accident and a recovery aided by the bond between girl and horse.

Another is the behind-the-scenes saga of the filming -- the grueling three-hour treks across the rocky peaks to get the horse and its five stand-ins to shooting locations on Sardinian beaches, the cobras that had to be milked to get rid of their deadly venom, the shipwreck shot in a tank.

The star, the central character that links these stories together is a horse, an 11-year-old Arabian stallion whose off-screen name is Cass Ole.

"We found him on a ranch here in Texas. He was named Cass because his father was named Cassanova. And when he was born, the Mexican help at the stable all shouted 'Ole!' When he stood up and whenever he did anything, they shouted ole, so he became Cass Ole," the horse's owner, 20-year-old Francesca Cuello, said in a telephone interview. "I was about ten when we bought him. I had ridden for a few years, but my parents thought that to go to the top I needed a good show horse. We had been looking around, but when they bought Cass out of the stall, that was it."

Franny Cuello, daughter of two Puerto Rican doctors who settled in San Antonio 13 years ago, rode Cass to the top of the showhorse circuit. Together, the two won about 500 ribbons and awards in every category from Arabian horses to ladies' sidesaddle. On the circuit, Cass caught the attention of Walter Farley, author of The Black Stallion and its sequels. When the producers of the film were trying to cast the title role, Farley recommended Cass. The filmmakers looked at horses in England, Morocco and Egypt before they came to the Cuello ranch.

"They watched Cass run around for a few minutes and that was it," recalled Franny. "I knew I'd miss him, but I had met the trainer, Glenn Randall, the man who trained Trigger, and I deeply trusted him not to do anything that might harm Cass."

So the contract was signed -- with a provision that said that the dangerous stunts would not be performed by Cass, who is insured by Lloyds of London for $250,000, but by doubles and stunt horses. In all there were six horses who appeared as the black stallion in the movie: an Arabian stallion named Faejur, who doubled for Cass in scenes that called for a wild, even vicious horse; two stunt horses owned by Randall, which performed such risky feats as jumping off a ship into a tank filled wit burning debris; and two horses from the Camargue area of southern France, which are seen in most of the swimming-in-the-surf scenes.

None of the horses is all black -- even Cass has four white socks and a white star on his forehead, which posed a real challenge to the make-up crew. Since there were so many water scenes, the horses were dyed with the same substance used in waterproof mascara.

After a training period with his three doubles on a California ranch, Cass went on location to Toronto, where the racetrack scenes and the scene where the horse escapes from Alec's yard and runs through the streets were shot; to Sardina, which served as the desert island; and to Rome, where the shipwreck scene was shot in a large tank in a studio. Franny Cuello, then a 17-year-old high-school-student, and her family, planned to fly to Italy to watch some of the filming.

"Nine hours before we were supposed to get on the plane for Europe, I was driving a pickup truck on the ranch and the tire blew out," said Franny. "The truck went into a ditch and rolled over. I had a brain contusion and was in a coma for 21 days."

When she came out of the coma, Franny couldn't talk, was almost completely paralyzed, and couldn't remember anything that happend in the months just before the accident. She did remember her horse, and riding Cass Ole again became a goal that helped but Franny back on her feet.

"When Cass was off filming, I thought a lot about him coming back," said Franny. "It gave me the incentive to rehabilitate myself so I'd be ready to ride him when he got back. I knew if I could ride Cass again, it would mean I had it together."

Two months before Cass was to return to the ranch, Franny, still in a wheelchair, was helped onto another horse and rode it a short distance. In December 1977, Cass came home and Franny was ready for him.

"Cass was fantastic. He seemed to sense something. He seemed to take care of me," she said. When the movie opened in New York, the Cuellos flew up for the premiere.

"It was like a dream come true," said Franny. "The horse you see in about 85 percent of the film is Cass, and I could always tell when it was him. All the loving scenes were Cass."

Today, Franny, who still limps a little but is almost completely recovered, is a student at Trinity University in San Antonio and plans a career as an accountant. She and Cass are back on the show circuit, when both have time, Cass is also an active stud, having already sired a couple hundred foals. Cass is also waiting in the wings to star in The Black Stallion Returns, -- the production of which has been delayed by the screen actors' strike. Only because of this production delay is Cass able to make the horse-show appearance. While the horse is here, he'll also attend a charity ball and visit the White House.

On opening night at the Capital Centre, Cass will gallop onto a simulated Arabian desert complete with other Arabians and riders in costumes supplied by the Saudi embassy. Scenes from the movie will flash overhead on the screen, and Cass, without the movie dye-job, will perform with his trainer, Margo Smith. Then a red carpet will be rolled out and Franny Cuello will walk into the areno. She'll mount Cass and ride him out of the ring. The thundering applause will tell her that she has it together.