At the top of the stretch, for a fleeting second yesterday, Affirmed's reaffirmation of his Kentucky Derby victory seemed in doubt.

Then Stveve Cauthen, astride the 1-to-2 Preakness favorite, and Joge Velasquez, aboard Alydar, really went to work. The two chestnut colts stormed through the Pimlico stretch in 18 1/5 seconds for the final three-sixteenths of the mile and three-sixteenths event, with Affirmed gaining a narrow victory.

It was one of the most memorable of the 103 Preakness races, and a record Pimlico crowd of 81,261 was there to see it. Affirmed' margin was a neck or, some observers thought, an eye. Once Affirmed saw Alydar trying to range up alongside, he never let him past.

This is the history of the two superb 3-year-olds. Their series record stands at 6-2, in Affirmed's favor, but Affirmed has won all the close ones. He defeated Alydar by a half-length in the Hopeful Stakes at Saratoga last August, by a nose in the Futurity Stakes at Belmont Park in October and, in their final duel as 2-year-olds, by a neck in the Laurel Futurity.

As has been the case in all their races, Affirmed and Alydar drew well away from their rivals. Believe It finished third, as he had in the Derby, only this time the distance between him and Alydar was 7 1/2 lengths, compared to the length and a quarter two weeks ago at Louisville.

Completing the order of finish in the nationally televised race were Noon Time Spender, Indigo Star, Dax S. and Track Reward.

Affirmed won much more comfortably at Churchill Downs, by 1 1/2 lengths. But his Preakness performance was equally convincing. This was a gut race, between two superb colts receiving two excellent rides.

The final time was 1:54 2/5, equaling the clockings of Seattle Slew and Secretariat. Only Canonero II ran faster here, 1:54 in 1971, but that mark is disputed because of a questionable timing system. Now Affirmed will bid, in the Belmont Stakes, to join Secretariat and Slew as Triple Crown victors.

The huge crowd made Affirmed its 1-to-2 favorite, Harbor View Farm's Florida-bred son of Exclusive Native thus returning $3 straight and combining with Calumet Farm's runner-up for a $4 exacta on the 6-3 combination.

Affirmed got $136,200 of the $188,700 purse, increasing his earnings to $1,023,227. He is the youngest millionaire in the history of thoroughbred racing.

"I want Alydar to hook Affirmed," trainer John Veitch said before the Preakness. "I think he's mature enough now to handle him, head to head, and I think the Affirmed people would like to see these two hook up, too, to kinda settle things."

Veitch got his wish. So did Laz Barrera, trainer of Affirmed. "If they hook, like I think they will, I'm confident Affirmed will win again," he said.

Velasquez offered no execuses.

"He ran a kind race, much kinder than in Kentucky, when he couldn't get ahold of the track until it was too late," Alydar's jockey said. "I was where I wanted to be. We were right with him (Affirmed) at the head of the stretch, but he wouldn't be passed. Alydar ran a fine race. He tried . . . Next time, I hope."

Eddie Maple, on Believe It, had much the same comment.

"We just can't get by Affirmed," he said. "My horse went to him about the three-eighth pole, but that other horse was pricking his ears, playing. Alydar might have intimidated us a little, when he went by. But that first guy (Affirmed) . . . you just can't get by him."

Alydar, Veitch and Velasquez got the fight they and Affirmed, Cauthen and Barrera had been itching for. All six likely will be on hand again at the Belmont in New York on June 10. The distance there will be a mile and a half as Affirmed attempts to become the 11th thoroughbred to sweep the Derby-Preakness-Belmont.

Indigo Star and Believe It broke on top, but when the seven 3-year-olds hit the clubhouse turn Affirmed was in the lead, followed closely by Track Reward and Believe It. Alydar was sixth.

Affirmed led the way into and down the backstretch, followed by Track Reward and Believe It. As they hit the half-mile pole, Alydar was beginning to move, and he passed horses on the turn to go into second behind Affirmed.

Then the duel that had been anticipated in the Kentucky Derby, but never really materialized, was on. They shot through the stretch, both Cauthen and Velasquez going to the whip as they drove their mounts toward the wire.

For a moment it looked as though Alydar might catch Affirmed, but the Harbor View Farm colt held on.

The triumph was further vindication for Barrera, who was criticized for racing AFFIRMED IN California before the Derby. Some critics said he was ducking Eastern colts such as Alydar and Believe It.

Affirmed has won all six of his starts as a 3-year-old and is in great position to add the 3-year-old championship to the 2-year-old title he won last year.

His career record stands at 13 wins and two seconds in 15 starts.