The Breeders' Cup at Hollywood Park Saturday will test the abilities of America's best racehorses and many from Europe. But it also is a test of an idea.

This seven-race program, offering a staggering $10 million in purses (WRC-TV-4 at 2 p.m.), was created to give the thoroughbred sport its own version of the Super Bowl or the World Series. It was designed to be a media event, one whose television coverage would win a wide new audience for racing.

To some extent, this bold idea of Kentucky breeder John Gaines has already succeeded.

Its centerpiece, the $3 million Breeders' Cup Classic, is a genuine championship event. Slew o' Gold -- a questionable starter until veterinarians successfully patched a crack in his hoof today -- will face Gate Dancer, Precisionist and five others, and the winner will be rightly hailed as the best horse in the country.

The $2 million Breeders' Cup Turf was weakened when injuries caused the defection of John Henry and Seattle Song. Even so, it has attracted four genuinely top-class runners from abroad -- Strawberry Road II, Alphabatim, Treizieme and 1983's Horse of the Year, All Along.

Yet the outcome of these races, and the other five $1 million stakes on the program, is probably less significant than the overall response to this day from the racing and television industries.

Does the Breeders' Cup generate enough enthusiasm to justify the damage it has done to so many well-established races? Can NBC present an engaging four-hour horse-racing telecast that can win a respectable audience? That will be the ultimate barometer of success or failure.

But the expected 60,000 spectators at Hollywood Park, as well as those at tracks across the country, including Laurel, who are betting on the simulcasted races, aren't going to be thinking about these long-range concerns. They can savor the excitement of handicapping and watching the greatest single racing card that has ever been presented in the United States.

The Breeders' Cup Classic, in particular, is a dramatic and intriguing showdown. Slew o' Gold came here after sweeping the fall championship series in New York, and was widely considered a cinch to nail down the Horse-of-the-Year title.

But when he arrived, Slew o' Gold was found to have a crack in the wall of his right front hoof which has given him trouble all year. This morning his veterinarians fitted the hoof with a fiberglass patch, and the 4-year-old went to the track to test it.

He passed the test with flying colors. After Slew o' Gold breezed three-eighths of a mile in 36 2/5 seconds, co-owner Mickey Taylor declared, "He was super. If everything stays the same, we'll start tomorrow."

But even if he is perfectly fit, Slew o' Gold will be subject to a tough challenge in the 1 1/4-mile Classic.

Gate Dancer, the Preakness winner who was best known for his purple earmuffs and erratic running habits during the Triple Crown series, has matured into a professional racehorse this fall. His victory in the $500,000 Super Derby was one of the most impressive thoroughbred performances of the year. His stretch-running style will be helped by the abundance of speed in the Classic field, as well as the newly rebuilt Hollywood track, which seems much less speed-favoring than racing surfaces in this state usually are.

As well-behaved as he is now, Gate Dancer still will wear his earmuffs Saturday. "Anybody can laugh at him," trainer Jack Van Berg said, "but as long as he keeps winning I'll do the laughing all the way to the bank."

In the other Breeders' Cup races:

Juvenile: Chief's Crown, syndicated this week for $20 million, should offer further proof he is the best of a weak lot of 2-year-old colts. His opposition in this mile race appears minimal.

Juvenile Distaff: Almost anybody could win this wide-open contest for 2-year-old fillies. Bessarabian has the seasoning, having won five straight races in the East, but Fine Spirit has the brilliance, which she showed in a 13-length maiden victory here. Outstandingly and Pirate's Glow are possible upsetters.

Sprint: "Everything this horse does is fast," says trainer Bud Lepman of his speedball Eillo. The colt has led all the way to win seven of his eight sprints this year, and Lepman has been pointing him all season for the richest sprint race in history. He tuned up by working a half mile in a sizzling 44 4/5 seconds.

Mile: If this turf race were run in England, Lear Fan would be an odds-on favorite. California bettors are more likely to prefer the horses with solid domestic credentials -- Royal Heroine, Cozzene and Tsunami Slew -- but Lear Fan is the class of the field. "I'm very pleased with him," said trainer Guy Harwood. He's there . . . he's on good form."

Distaff: The quality of the field is very high; Life's Magic, Lucky Lucky Lucky, Miss Oceana and Adored are all multiple stakes winners. Even so, nobody figures to beat the rejuvenated Princess Rooney, who annihilated some of these same rivals in the Spinster Stakes at Keeneland last month. She will be the shortest-priced favorite of the day.

Turf: All Along hasn't won a race since she was voted America's Horse of the Year in 1983, but she seems to be returning to her best form. She might get her major opposition from Strawberry Road II, who was the victim of a horrendous ride in the Washington, D.C. International and is overdue for a little bit of good racing luck. Maybe $2 million worth.