A 3-year-old colt named Sain Et Sauf makes his long-awaited racing debut at Gulfstream Park Saturday, but anything he does on the track will be an anticlimax compared with his prenatal adventures.

While he was still in the womb, Sain Et Sauf's mother was kidnapped, abandoned, sought by the FBI and presumed dead. Despite her million-dollar pedigree, she was almost sold for slaughter for a few hundred dollars.

The dam, Fanfreluche, had been Canada's horse of the year in 1970, and when her racing days were over she began an equally distinguished career as a broodmare. She had foaled four stakes horses, including one Canadian champion, before she was bred to Secretariat in 1977.

It was on a day in June that year that Fanfreluche disappeared without a trace. Employes at Claiborne Farm in Lexington, Ky., found a hole cut in the fence of her paddock. Investigators deduced that she had been led down a lane to a wooded area and loaded into a horse trailer. But the trail ended there, and the disappearance of the mare because a cause celebre in Kentucky's breeding country.

The case was not news in the backwoods area around Tompkinsville, Ky., where Larry and Sandra McPherson were awakened one Sunday by a phone call from a neighbor who reported, "Your horse is loose." In Tompkinsville, this was nothing uncommon; livestock often are found wandering around the neighborhood. But when the McPhersons went outside to investigate, they saw that this was no mare of theirs.

"She was in very bad condition," Mrs. McPherson said by phone today. "You could tell she'd had some rough treatment. You could count her ribs. We figured she was just an old farm horse, so Larry put out the word that we'd found her, and put up a notice in the country store. We took her in and fed her like one of our own horses."

As the newcomer's condition improved, Mrs. McPherson took her out for occasional rides through the woods and fields near their home but she said "The mare wasn't a good riding horse. When you were on her, she knew what to do, but she was kind of high-spirited when you'd ride; more than I like. She was very rough.

"Some of Larry's friends tried to trade for her," Mrs. McPherson remembered. "They offered a good riding horse for her. They wanted to take her to a poundage sale in Tennessee. She probably would have sold for $200 or $300, but Larry told them she wasn't his to trade."

The McPhersons kept the mare, whom they called Brandy, for six months, noticing only near the end of that period that she showed signs of being pregnant. Then one night in December, an FBI agent appeared at their door, accompanied by the owner of Claiborne Farm, and said he was investigating the disappearance of a thoroughbred named Fanfreluche. Could he look at the mare who had wandered onto their property?

That marked the end of Fanfreluche's adventure, although many questions about the kidnapping have never been fully answered. A suspect in the case was arrested but never brought to trial; investigators thought he may have lost the nerve to carry out whatever plan he had conceived and turned the mare loose somewhere in the vicinity of Tompkinsville.

Fanfreluche gave birth the next spring, and Jean-Louis Levesque, the wealthy industrialist who owned her, staged a contest to name the foal. The winning entry means "safe and sound."

Since his birth, Sain Et Sauf's only problems have been ordinary equine difficulties. He's had quite a lot of trouble with his ankles," trainer John Starr said. "But if he stays healthy, I think he'll be a good horse." On Saturday, they will begin to get an idea of the colt's value.

But the McPhersons know what the value the colt had to them zero. They never got so much as a thank-you note from Levesque for taking care of his prize possession, much less a reward. "All we got was the feed bills," Mrs. McPherson said.