The field for Thursday's Blue Grass Stakes illustrates a great change in the way trainers prepare a horse for the Kentucky Derby.

It used to be axiomatic that a 3-year-old needed a tough race shortly before the Derby to bring him into razor-sharp condition. Some horsemen loved to use the Derby Trial -- run only four days before the main event -- for this purpose. But it was the Blue Grass, a 1 1/8-mile race nine days before the Derby, that seemed the ideal prep race.

In the 14 years from 1959 to 1972, nine horses who ran in the Keeneland event wound up being draped with roses at Churchill Downs. But in the past decade, trainers increasingly have wanted their horses to come into the Derby fresh and rested, and the Blue Grass has fallen out of vogue.

This year, the two favorites for the Derby, Snow Chief and Badger Land, ran their final prep races on the first weekend in April -- four weeks before their main objective. The horses in the Blue Grass are mostly ones who are getting a last-ditch shot to prove they belong in the Derby lineup.

The most intriguing entrant in the Blue Grass lineup is Bold Arrangement, a colt from England who will be making the first start of his career on a dirt track. Bold Arrangement has the necessary class -- he lost a photo finish in France's most important 2-year-old race last season -- but the grass-to-dirt transition is a tough one.

Unless Bold Arrangement makes an impressive shift to this unfamiliar game, the horse to beat in the Blue Grass is probably Bolshoi Boy. The gelding finished four lengths behind Badger Land in the Flamingo Stakes at Hialeah -- and Badger Land's performance that day was perhaps the fastest and best of all the Derby preps.

Another contender is Icy Groom, who finished second to Snow Chief in the Santa Anita Derby. His trainer, Eddie Gregson, was the last man to use the Blue Grass successfully as a prep for the Kentucky Derby. Gregson won the 1982 Derby with Gato del Sol, and he thinks the lightly raced Icy Groom may be improving fast enough to duplicate that feat.

The rest of the field includes Bachelor Beau, The Flats, Pillaster, Strong Performance, Major Moran, Big Play, Blandford Park and Blue Buckaroo.