The only thoroughbred before Seattle Slew to advance two-thirds of the way toward the Triple Crown and still be undefeated was Majestic Prince, in 1969.

He was owned by Frank McMahon, a Canadian oil and gas multimillionaire who paid a record $250,000 for the chestnut colt at the Keeneland yearling sales. The trainer was Johnny Longden, the hall of fame.jockey. The jockey was Bill Hartack.

Longden delayed Majestic Prince's first start until the fall of the horse's 2-year-old season. He won, then won another baby race and was ready for a demanding winter campaign at Santa Anita.

Victories in the Los Feliz, San Vicente, San Jacinto and Santa Anita Derby opened the '69 season. Then it was on the Churchill Downs and an eye-opening success over Fast Hilarious, at top sprinter, in the seven-furlong Stepping Stone Purse.

Favored in the Kentucky Derby, Majestic Prince downed Arts and Letters by a neck in an outstanding field of eight that included top Knight and Dike. The Preakness was next, Majestic Prince scoring by a head over Arts and Letters at 3 to 5.

Longden had trained the colt masterfully, to a perfect record, through nine races. Then the owner took over.

"Majestic Prince is developing a little trouble in his right front," Longden had told the press in Pimlico's track kitchen the morning after the Preakness. "We'll be back here in the East with him in the fall but Mr. McMahon agrees with me that the right thing to do now is take him home, to California, for a little rest. He wouldn't be able to run his best in the Belmont."

The next morning, reached by telephone in Florida, McMahon agreed with Longden's appraisal of the colt's physical condition.

"We want a Triple Crown, not a Crippled Crown" the owner said. "John is right. The horse is going home."

Majestic Prince was booked on a plane leaving the Baltimore airport late that Monday night. Everything was ready, only to have the plane filled with critical war material for Southeast Asia that bumped Majestic Prince off the flight.

By the time Tuesday night's plane was to have departed there had been a change in plans. McMahon suddenly announced Majestic Prince would be sent to New York for the Belmont.

The older statesmen among the nation's press were quick to praise the owner and criticize the trainer. McMahon clearly was a sportsman, they suggested, while Longden was a chicken trainer who had been responsible for breaking down the brilliant Count Fleet the day he completed the Triple Crown in winning the 1943 Belmont by 25 lengths.

When Longden and McMahon met in New York, several days before the Belmont, they had a sharp exchange of words, privately, off in a far corner of one of the spacious barns on the Belmont backstretch. But that was all. From then on Londen's public utterances followed the McMahon line.

Arts and Letters whipped Majestic Prince by 5 1/2 lengths in the Belmont. Some observers said the Derby and Preakness runner-up had the better pedigree for a mile-and-a-half. Many others criticized Hartack, always a favorite whipping boy, for what they considered a poor ride on Majestic Prince.

The truth was Majestic Prince was hurting. Arts and Letters was a superior horse in excellent hands but I doubt he could have beaten Majestic Prince doing anything when Majestic Prince was right.

Longden finally was able to take Majestic Prince home to California after the Belmont. The trainer never invoked an alibi for the defeat, never was critical of the owner.

"I tried to bring Majestic Prince back to the races later that year," Longden recalled yesterday from his California home. "The same trouble started all over again so he was retired (to Spendthrift Farm in Lexington, Ky.). The trouble was what they call a check ligament, behind the knee down to the tendon."

Now it's Seattle Slew, with only one fewer victories than Majestic Prince coming into the Belmont.

Seattle Slew has one obvious advantage over Majestic Prince as he approaches Saturday's 109th Belmont against six probable rivals.

"The only way Slew can get beaten is if we beat him," owner Mickey Taylor said after the Preakness. "It is the people around this good a horse, not the horse itself, that gets him beaten. We're never going to run Seattle Slew in a race unless we're confident he's capable of running his best."

Seattle Slew worked six furlongs in 1:11 3/3 yesterday at Belmont. The Bold Reasoning colt should have no excuse Saturday in his bid to succeed where Majestic Prince failed.