The Brooklyn Handicap has long been a showcase for the best older horses in America. But when it is run for the 94th time at Belmont Park today, casual racing fans will be forgiven if they don't recognize the names of the principal contenders.

It's the One is expected to be favored over John's Gold, a 3-year-old filly, a confrontation that will not remind anybody of Damascus versus Dr. Fager or Forego against Foolish Pleasure. Although the complaint has been heard for years that good thoroughbreds are retired too quickly, depriving the sport of its box-office attractions, the problem has become critical in 1982.

There are no good older horses in the Brooklyn Handicap because there are almost no good older horses in training anywhere, despite the fact that last year's 3-year-old crop was a deep one. The lineup for the Travers Stakes at Saratoga included six colts with excellent credentials: Pleasant Colony, Lord Avie, Noble Nashua, Five Star Flight, Summing and Willow Hour.

If even a few of them were in action now, they would be enlivening the current racing season. But all have been retired to stud.

Until recently, competitive life did not have to end at 3 for top-class male racehorses; Seattle Slew, Affirmed and Spectacular Bid all raced at 4, winning a lot of money and generating a lot of excitement.

But the racing business has been changing drastically. As more buyers have come to view high-quality thoroughbreds as good investments, hedges against inflation and tax shelters, the prices for these animals have soared to levels unimaginable a few years ago. Yearlings have been sold for as much as $3 million, stallions syndicated for as much as $30 million. What a good horse can earn in purse money is trifling compared with what he can earn in the breeding shed.

Modern day economics almost demands that an owner retire an outstanding colt early. In fact, an owner would have to be irrational to race a champion at 4, risking his reputation while paying enormous insurance premiums, when the horse could spend that year servicing 40 mares for a stud fee of $100,000.

Not only are top horses being retired young, but the boom in bloodstock prices will surely encourage owners to race them less and subject them to fewer risks. Traditionally, American horses have had to pass rigorous tests, such as the grind of the Triple Crown series, to be accepted as champions. But breeders are now so eager to syndicate stallions that a horse can elicit multimillion-dollar offers on the basis of a few achievements.

Storm Bird was syndicated in Europe for a reported $30 million on the basis of a five-for-six record as a 2-year-old; he was retired early in his 3-year-old season.

Conquistador Cielo displayed brilliant form from Memorial Day to July 4, enough to attract a syndication offer of $40 million -- more than the combined syndication prices of the last three Triple Crown winners.

These trends are, of course, terribly unhealthy for the racing business, although until recently no one had any ideas about how to combat them. This spring, however, Kentucky breeder John Gaines made a proposal that was stunning in its originality and boldness.

"Racing needs a version of the World Series or the Super Bowl," he said, and so he proposed a day of racing to be called the Parade of Champions, which would consist of very rich events for all categories of horses, with purses for individual races as high as $5 million.

Under Gaines' plan, breeders would pay a sum equal to one-half a stallion's stud fee to make all of his progeny eligible for these championship races. He calculated that this formula would raise $15 million in purse money. With this kind of money available, owners would finally have a financial incentive to keep good horses in training.

It is still uncertain whether Gaines can get enough support from other breeders to make his vision a reality. But something dramatic must be done to keep good older horses on the track, and to keep the sport exciting and competitive. Otherwise, more and more supposedly "classic" races are going to turn into drab affairs like today's Brooklyn Handicap.