Ah, the mystique of H. Allen Jerkens.

To see the reporters, young and old alike, follow the Hall of Fame trainer through the back stretch at Churchill Downs these mornings is something to behold. They write down his every sentence, hanging on his every word and nonword, waiting for more and, while Jerkens has become much less reserved with the press in recent years, he will never be classified as talkative.

But Jerkens is "the genius" of American horsemen. So they wait, and hope, and listen. This, after all, is the man, the son of an Austrian cavalry officer, who beat Buckpasser with Handsome Boy who beat Secretariat with Onion, who beat Secretariat again with Prove out and, in lesser achievement, beat Forego when he was a 3-year-old with Step Nicely. He consistently wins races with other trainers' rejects and with obviously less talented runners. He is special. He entourage tells you that.

Only once before in 28 years of training has Jerkens tried the Kentucky Derby, saddling Round Stake in 1975. That was an experiment. Round Stake finishing 11th to Foolish pleasure at odds of 55 to 1. This time he is serious, with Sensitive Prince, the undefeated colt that will be the solid third choice to Alydar and Affirmed here Saturday in the 104th running of the Run for the Roses.

Yesterday morning shortly before sunup, the Great One led Sensitive Prince to the track for his last important Derby workout. "He'll move right along," the trainer had promised the day before. "I'd say he'll go in 24 to 25."

Sensitive Prince cruised through an opening quarter in 25 flat, continued that pace through a half-mile in .50 accelerated slightly to .12 4?5 and .12 for the next two-eighths of a mile, then finished out seven furlongs in 1.27 4?5 and a mile in 1.41 4/5.

The time could not have been what Jerkens ideally wanted. Sensitive Prince had not worked particularly last, [WORD ILLEGIBLE] finished particularly strong. Yet, "He did just what we wanted," the trainer told the assemblage. "He galloped out strong and wasn't blowing when he came back."

Sensitive Prince has won six races, the last five for Jerkens this year. But he has been tested only once for quality, in the Fountain of Youth Stakes at Gulfstream Park on March 22. The athletic-looking bay son of 1969 Kentucky Derby winner Majestic Prince defeated Believe It by a head that day. He was in receipt of eight pounds from the runner-up, however. In the Derby, Believe It is the fourth choice among 10 anticipated starters, all of whom will carry 126 pounds over the mile and a quarter.

Jerkens' horse never has been farther than a mile and a sixteenth. His game is on the front end, which is exactly where longshot Raymond Earl figures to be for the first half-mile Saturday. There are those who believe Sensitive Prince is not ready for such a long, demanding trip. There are others who swear that Jerkens could get a Missouri mule up to a snappy 10 furlongs if he had to.

"I'm pretty sure he's going to run good, Jerkens keeps saying, although he appeared to be a trifle less certain after yesterday's work.In fairness, the trainer has had certain unusual problems to contend with in training this horse.

Joe Taub, the owner, recently sold a share of Sensitive Prince to Dennis Milne, an Ohio veterinarian. "Both partners are licensed," says Keene Daingerfield, state steward. "They filled up a partnership application which indicates Mr. Taub is a large stockholder in the colt and Dr. Milne has a small share." The small share reportedly is one-tenth.

Jerkens apparently has had to train Sensitive Prince to meet a certain situation. He acknowledged this week that he would have preferred running the horse in the Wood Memorial in New York, as a final prep for the Derby instead of shipping to Keeneland for an overnight race. But it was important, the trainer indicated, for the colt to continue to be undefeated.

The reason for being so concerned about Sensitive Princes' unbeaten status undoubtedly had to do with his potential selling price. A defeat before the Derby would have lowered that price considerably.But Taub continus as the principal owner and, now the colt may have been deprived of the logical Derby preparation he needed.

Still, there will be plenty of action on Sensitive Prince against Alydar and Affirmed. An undefeated horse always has particular appeal to many betters, especially those who remember Seattle Slew was six for six when he scored here last spring.

There was one important difference, however.Seattle Slew, lightly raced like Sensitive Prince, had been much more thoroughly tested and the Derby competition was considerably weaker. Sensitive Prince's situation is much more comparable to that faced by No Robbery when he arrived here in 1963 to put his undefeated record on the line against Chateaugay, Never Bend and Candy Spots. The crowd made No Robbery the second choice to Candy Spots but he faded to fifth place.

The 1978 field appears to be the strongest to assemble here since 1963. So Sensitive Prince better be as ready as Jerkens can make him.

"You get a little embarrassed, people keep talking (about his reputation) even when you're not doing well," the trainer said, alluding to his recent slump. "People are still saying those things. Some (of those miraculous upsets he masterminded) are just luck or premonitions, and you put a horse in a certain race.

"But one thing I've learned: it never pays to take a shot unless the horse is doing exceptionally well at the time."

Sensitive Prince has responded beautifically to Jerkens' care. All that remains is for the colt to run as well as Jerkens trains. That is asking a lot, but the disciples believe in their man. They will be betting on Jerkens more than on Sensitive Prince. Off his record and his reputation, they have a right.