Never in the history of the Triple Crown have there been back-to-back winners.

One years separated Omaha and War Admiral, Whirlaway and Count Fleet, Assault and Citation, while Sir Barton, Gallant Fox and Secretariat are rather isolated on thoroughbred racing's most prestigious calendar.

But today, if the favorite players are correct, Affirmed will follow Seattle Slew into the elite company by adding the Belmont Stakes to his victories in the Kentucky Derby and Preakness. All Affirmed has to do is to prevail over the 1 1/2 miles of the Belmont and Harbor View farm's handsome chestnut colt will become the 11th Triple Crown hero.

It will not be easy.

Winning always is a difficult assignment when Alydar is around, and the Calumet Farm's runner is primed to try Affirmed again. Darby Creek Road, Noon Time Spender and Judge Advocate complete the field but it is Alydar, at even money, which is accorded a strong chance of denying the 2-to-5 favorite an automatic place in the turf Hall of Fame.

"I'm confident again," trainer Laz Barrera declared this morning at Affirmed's barn on the Belmont Park backstretch. "Alydar is a helluva horse. I tell you, Native Dancer (the grandsire or great-grandsire) put a lotta class into these two colts. But I tell you this: as long as Affirmed can see Alydar, he play with him, like a cat play with a mouse.

"He see him come on, and then he let out a little bit. My horse run just fast enough never to let the other horse get by."

Barrera made a similar observation before the Preakness and Affirmed turned the Cuban-born conditioner into something of an oracle, gamely holding off Alydar through the stretch to score by a long neck. Affirmed captured the Derby much more easily, by a length and a half.

"Alydar didn't run his race at Churchill Downs. At Pimlico, he did; it just wasn't good enough," commented John Veitch, the young Calumet trainer. "Now, in the Belmont, conditions swing to Alydar's advantage. This is a test of strength and stamina. Alydar is the stronger colt. We are going to try to grind Affirmed down over the final five furlongs."

The blinkers are coming off Alydar.This could help, but the Calumet forces are even more encouraged by what they think they see in Affirmed's training since the Preakness three weeks ago.

"These races in the Triple Crown take a lot out of a horse, being so difficult, and being run in three different locations," a member of the Alydar entourage noted. "Affirmed has not survived the rigors of this campaign as well as, say, Secretariat did. He is down slightly in flesh and he has not been galloping as freely, nor as strongly, for this race as he did in Louisville and Baltimore."

Barrera scoffed at such comments. He saddled a sprinter, Bold Forbes, to win the Belmont two years ago. Affirmed, he assures, is much better equipped to negotiate today's 12-fur-long distance than most Derby and Preakness winners.

"What beat most of those horses when they lost the Triple Crown in the Belmont, was soundness" Barrera declared."Forward Pass wasn't sound when he lost (to Stage Door Johnny in 1968), Majestic Prince wasn't sound when he lost (to Arts and Letters in 1969) and Canonero wasn't sound when he lost (in 1971).

"Affirmed, my friends, is sound." Sound of limb and sound of (jockey's) mind. Steve Cauthen, at 18 is going on 35, rarely makes mistakes in a race, and his performances aboard Affirmed this spring have been flawless. There is always the possibility Cauthen and Jorge Velasquez Alydar's excellent rider, could become too involved with each other, permit their mouths to go too fast too early, and be beaten by Darby Creek Road.

But the chances of that happening are longer than the odds on the three longshots. From the five-eighths pole to the finish line, this 110th Belmont figures to be one of the most exciting match races in the event's dramatic history, without any outside intervention.

Darby Creek Road, fourth in the Derby, passed the Preakness in order to have a better chance in the Belmont. Angel Cordero, often a brilliant tactical jockey in these situations, has the riding assignment.

Noon Time Spender and Judge Advocate are out of their element.

First money is $110,580 from the $184,300 purse. Affirmed already is a millionaire, the youngest such runner the sport has seen. Alydar's earnings total nearly $700,000.

A crowd of 60,000 to 70,000 is expected to attend today's program in beautiful weather. The track will be fast. CBS will televise the proceedings nationally from 5 to 6 p.m. The only familiar figure missing will be Believe It, the third finisher in the Derby and the Preakness.

"We're going elsewhere, to Ohio or Illinois," trainer Woody Stephens repeated yesterday. "Somewhere Affirmed and Alydar aren't. In another year. Believe It probably would have won one or two of these classic races. He just came along at the wrong time.

"In the Derby, Believe It went up alongside Affirmed, on the stretch turn, but couldn't get past him. Believe It challenged Affirmed even earlier in the Preakness, with the same result . . . You've run into an iron wall when you get up to him." tr for add seven

That is a beautiful description of Affirmed, a colt that appears to have the uncanny ability of measuring his closest rival, whoever it may be. Affirmed and Alydar have met eight times. Affirmed holds a 6 to 2 advantage. If he can make it 7 to 2, the strain will have been worth it, because no one will ask - as many observers often do of Triple Crown heroes - "Who did he beat?"

The answer will be obvious. He beat Alydar.