Ordinarily, the best 3-year-olds from the East, West and South don't face each other until the Kentucky Derby. But a major intersectional match up will occur earlier this year, in Thursday's Blue Grass Stakes at Keeneland, and the winner probably will be the favorite at Churchill Downs next week.

From California come Marfa, the early Derby favorite, and Desert Wine, who had that status until Marfa trounced him in the Santa Anita Derby.

From Maryland, Deputed Testamony and Noble Home.

From Florida, Copelan and Play Fellow.

From Kentucky, Highland Park.

"This race is going to be a pretty good gauge of what's going to come later," said Wayne Lukas, Marfa's trainer. "But this is more than a prep race. This is a showcase, with every breeder in the country in the stands. We want to win the Blue Grass."

Indeed, this is the best and most fascinating 3-year-old race of the year to date. It is likely to expose the shortcomings and spurious reputations of a number of big-name horses. And it may well bring to prominence the Maryland colt, Deputed Testamony, whose reputation is currently nil.

The most likely to flop Thursday is the local favorite, Highland Park, who has won five straight races in Kentucky. Trainer Tony Basile insists his colt is underrated, but, in fact, he has been beating mediocre horses narrowly and has never shown he is in the class of his Blue Grass rivals.

Copelan and Desert Wine also are doubtful propositions. Copelan is a tough, gritty competitor, but he has not shown he can go the Blue Grass distance, 1 1/8 miles. Desert Wine ran so badly in his last start in California that his physical condition may have deteriorated since his good, early season races.

But Deputed Testamony and Marfa both appear to be coming into this race in peak condition. The Maryland colt looked impressive winning his last start at Pimlico. His time was so fast that some handicappers wondered if it could somehow be a fluke. Their doubts mounted when Minabchar, who had finished respectably close to Deputed Testamony at Pimlico, ran in New York today and was soundly beaten in an allowance race. Deputed Testamony will remain an unknown quantity until Thursday afternoon.

Marfa, however, is a known quantity. Only three months ago, he was having trouble winning allowance races. But Lukas kept insisting the colt had considerable ability. "We knew there was octane in the tank," he said. Marfa finally lived up to his trainer's hopes when he won the Jim Beam Spiral Stakes at Latonia by eight lengths, then captured the Santa Anita Derby decisively.

He might be slightly hampered in the Blue Grass by one change that Keeneland officials have made to accommodate the 13-horse field. So that the horses will have a longer run to the first turn, the race will start a sixteenth of a mile before the usual position for the gate and end a sixteenth of a mile before the normal finish line. A stretch-runner like Marfa certainly might be hurt by the shortened stretch. But he may offset this disadvantage by being the best horse in the sharpest condition.