Lean and handsome Tim Jecko, a 19-year-old Yale sophomore from Bethesda, Md., has made it plain during the last fortnight that he is fast becoming one of the world's top swimmers. In the NCAA championships at Chapel Hill, N.C. he set two records and was a triple winner. Last week, during the AAU championships at Florida's Daytona Beach, he won the 400-yard individual medley (in which a swimmer must do 100 yards each of butterfly, backstroke, breaststroke and freestyle) in 4:39.2, the fastest time ever made by an American. He was beaten at his favorite stroke in the 100-yard butterfly, but in losing he demonstrated that he is worthy of succeeding the victor, Ohio State's incomparable Al Wiggins, who is certainly one of the world's three most versatile modern swimmers but who is soon to devote himself to the study of law. World Record Holder Wiggins was only a yard ahead at the 50-yard mark, had to sprint from there to the finish to stay in front of young Jecko, who is the only other man on earth to have broken 55 seconds for the event. As they stood together after the race Wiggins grinned and said: "I don't ever want him this close to me in the water."