The Kentucky Derby said hello to Steve Cauthen and, quite possibly, good-bye to Calumet Farm yesterday as the sensational 18-year-old jockey guided Affirmed to a 1 1/2-length victory over the devil's red and blue Alydar in the 104th running of America's most popular horse race.

Affirmed held off Alydar after Cauthen gunned him past Sensitive Prince and into the lead on the stretch turn. Believe It attempted to move with the winner, but could not keep up through the lane, fading to third place, 1 1/4 lengths behind the favored Alydar.

Affirmed the second choice of the 131,004 fans, paid $5.60 straight after completing the superbly contested 1 1/4 miles in 2:01 1/5. That tied as the fifth fastest derby in history.

Cauthen is not the youngest rider to win the Derby. That distinction still goes to Bill Boland, who jockeyed Middleground to 1 1/4-length victory over the highly regarded Hill Prince in 1950. Boland was a 16-year-old apprentice.

But Cauthen, the "Stevie Wonder" from Walton, Ky., some 80 miles northeast of here, turned in a letter-perfect effort on Affirmed. He had last season's champion 2-year-old off alertly from the No. 2 position in the starting gate, permitted Raymond Earl and the previously undefeated Sensitive Prince to set a pace of 1:10 4/5 to the far turn, then to establish a daylight advantage that not even the furious closing finish of Alydar could overcome.

Calumet was trying for its ninth Derby victory. Alydar valiantly carried the famous colors of Gene and Lucille Markey, both of whom are in their 80s and watched the race from wheelchairs at their Lexington, Ky., farm.

So Calumet failed, in what probably was its last bid to add to the fantastic Churchill Downs record established by Whirlaway, Pensive Citation, Ponder, Hill Gail, Iron Liege, Tim Tam and Forward Pass.

Affirmed's success also was a fast-moving tribute to Cuban-born trainer Laz Barrera who saddled Bold Forbes to defeat the 2-to-5 favorite, Honest Pleasure, in the 1976 Derby. Barrera had Affirmed trained up to the moment for this race, just as he had last year when the Harbor View Farm colt defeated Alydar in four of their six meetings.

There was some doubt, however, that Affirmed would be as sharp as Alydar yesterday. The chestnutson of Exclusive Native had won all four of his races in California, but in less impressive fashion than Alydar captured his four outings in Florida and Kentucky.

Thus $1,501,236 was bet on Alydar in the win-place-show pools, compared to $1,242,322 on Affirmed. It marked the first time two horses had attracted more than a million dollar play. This Derby attracted a record $4,425,828 parimutual handle.

Cauthen's assignment was to keep Affirmed in touch with the early speed, to move at precisely the right time with, or before, Believe It - and then to have enough horse left to withstand Alydar.

"Don't let him pounce on you like he did in the Champaigne last fall," Berrera repeatedly warned Cauthen this week. "Make sure Affirmed is able to see him. The trouble, in the Champaigne, was that Affirmed was in between horses, Alydar roared by and was way in front before Affirmed could see them . . . and go after him."

Cauthen followed orders well. Believe It, on the outside, had his head in front for a stride or two colts swung into the home stretch. But Cauthen had timed Affirmed's attack perfectly. He was inside Believe It and had been able to easily swing his mount to the outside, past the tiring Raymont Earl then past Sensitive Prince at the top of the lane.

"From there, it was just a matter of keeping him going, making sure he didn't let up," Cauthen said."We knew Alydar would be coming at us. He always is. But I was confident Affirmed could hold him safe. He usually has."

Jorge Velasquez turned in a sound effort aboard Alydar. The Calumet colt was far back during the early moments, but began to pick up rivals during the long run up the back stretch and was fourth - less than five lengths behind Beleive It and Affirmed - at the end of a mile in 1:35 4/5.

"He just couldn't get hold of the track," Velesquez said. "He didn't start to run until the last eighth of a mile. The track was just too hard."

Alydar was expected to come from behind, so the crowd wasn't bothered when he settled near the back of the pack in the first rundown the stretch. But Velasquez had already sensed trouble.

"He didn't have running on his mind," Velasquez said. "I didn't plan to be that far back."

And when Alydar, as expected began passing horses, he wasn't making up ground on Affirmed.

Bobby Baird, the rider of 10th-place Raymond Earl, knew Alydar was through when he saw the Calumet colt.

"He was in a stone drive just like he was in the Blue Grass," said Baird, whose amount finished 13 1/2 lengths back of Alyder in the Blue Grass Stakes nine days ago. "He (Alydar) was all used up."

Added Velasquez: "He was passing horses on the turn, but he still wasn't running. I knew at the half-mile pole that I didn't have time to catch whoever was going to win it."

Alydar simply was not good enough, although the 104th Derby had been run to the anticipated pattern, which showed virtually every move as likely to be to the advantage of the big horse making the last run.

If yesterday's Derby was the likely end of a long line of success for Calumet, it was also the end of an even longer line of frustration for Patrice Jacobs Wolfson, wife of Lou Wolfson, Affirmed owner. Her father, the late Hirsh Jacobs, was represented by nine Derby runners. Palestinian, Our Dar, Dr. Miller, Bonjour, Flag Raiser, Exhibitionist, Reason To Halt, High Ecvhelon and Personality all failed. None finished better than third.

And the Jacobses' best colt, Hail To Reason, broke down near the end of a brilliant season as a 2 year old. But yesterday "Darlin' Patrice" could thank a superior colt, a wonderful veteran trainer and a young race rider the likes of which this country has never seen before.