Seven rivals were in the starting gate with Seattle Slew for the Belmont Stakes, but in the minds of many of the 70,229 fans who turned out for the historic occasion the horse they wanted their undefeated hero to beat Saturday was not among them. Secretariat retired in 1973.

"Seattle Slew might even be better than Secretariat . . . if he tried a little harder," one young bettor declared as he waited for the 2-to-5 favorite to appear in the Belmont Park paddock.

Many fans believe this. Or at least they want to believe.

Seattle Slew went forth and led throughout the 1 1/2 miles of the Belmont, scoring by four lengths and thus becoming the first of the 10 Triple Crown winners to advance so far so perfectly. His performance was more than adequate by any standards, yet it failed to thrill many of the professional horsemen in the huge audience.

"As an achievement, his Belmont will go down as ranking right alongside Avatar's," one trainer said. Avatar, the 1975 winner, was a nice colt. Nobody, however, ever accused him of being great.

Seattle Slew's time of 2:29 3/5 was not Secretariatlike (2:24). The track, listed as muddy, actually was what New Yorkers love to call wet-fast. Earlier times on the program were good. Seattle Slews was ordinary.

So, for that matter, was the way he and jockey Jean Cruguet achieved their victory.

"There was no pace," cried Jacinto Vasquez, rider of Mr. Red Wing. "Those jocks didn't go after him."

That's right. They didn't.

Spirit Level, Run Dusty Run, Sanhedrin and Iron Constitutionall made semiserious probes at the frontrunner but none ever attempted to blast Seattle Slew out of the lead. They were content to piddle-paddle along, letting the best horse dictate all the fractions.

The only real excitment was provided by Cruguet, who decided to stand up and give the crowd a victory salute 20 yards before the finish.

Surely, Run Dust Run, Sanhedrin and Iron Constitution must know by now that Seattle Slew is the best of his generation. Cormorant is the only 3-year-old that can be excused for wanting another try, for refusing to accept the preakness as a 100 per cent true bill.

The Travers at Saratoga on Aug. 20 may be Seattle Slew's next race. Bold Reasoning's brilliant son is about to get a well-deserved rest. After the Travers there will be the Woodward, the Marlboro and, perhaps, the Jockey Club Gold Cup or the Washington, D.C. International. Racing's championship season, usually ignored by much of the media, may finally receive the serious attention it deserves.

Seattle Slew now has nine victories in nine starts, $717,720 in the bank, a $12 million value as a future stallion - and Forego waiting for him in the fall.

Forego has been Horse of the Year since Secretariat retired in 1973. The 7-year-old gelding will provide the ultimate test for the sport's newest glamor boy. If Seattle Slew can beat this gallant old warhorse there will be no denying him a special niche in the Hall of fame.

Secretariat holds such a spot, in my opinion, although it is surprising how a few observers have omitted him recently from their lists of "top 10" or "great" runners.

If Secretariat didn't merit that adjective, which should be employed oh so rarely, then I never saw a race horse that did. All three of Secretariat's Triple Crown races were superb, memorable efforts, both from the standpoint of style and time. Sham, his main rival, was an excellent colt.

Only in the Preakness did Seattle Slew approach any of Secretariat's Triple Crown achievements. The Preakness was Seattle Slew's best race. He will have to duplicate it in order to handle Forego.

I am always suspicious of any horse, past or present, that made his reputation solely by beating the same members of his generation, over and over, under level weight. The greatest challenge usually comes when the champion 3-year-old goes up against older horses. Secretariat passed this test, too, by defeating Riva Ridge and an excellent field in the 1973 Marlboro.

Seattle Slew did not measure up to Secretariat Saturday. The only thing about this Belmont that was superior to the '73 running was the size of the crowd it attracted. But from here on Seattle Slew will have an opportunity to advance on Secretariat every time out. Secretariat's late summer and fall form was spotly.

It would appear Seattle Slew is going to be better managed than Secretariat was, yet he is not about to duck anyone. His owners and trainer have supreme confidence in their colt's ability and they appear to be as game as he is. They say Seattle Slew will face Forego in the fall, then return as a 4-year-old to carry high weight in the 1978 handicaps.

This is something Secretariat never attempted. So, by the time Seattle Slew is retired, we should know rather precisely just how good, or how great he was.

Until then it should suffice to saye of Seattle Slew, simply: "He wins." He has never lost, and he has completed the Triple Crown.

There are worse ways to begin a career as a race horse.