John Winnett and his 15-year-old Hanoverian gelding, Leopardi, won the Grand Prix event yesterday at the Potomac Horse Center dressage competition and U.S. Equestrian Team Olympic screening trials.

Winnett, 51, of Tuxedo Park, N.Y., has competed internationally since 1953 when he represented the United States at the World Jumping Championships in France. He earned a mark of 60.87 percent, edging Linda Zang of Davidsonville, Md., who had 60.53 on her Swedish half-bred, Fellow Traveler.

Dressage, the art form of equestrian competition, is scored much like figure skating, with points awarded for each intricate movement.

"We're both probably the oldest ones here," said Winnett, a manufacturer of horse equipment and an accomplished golfer. "But he (the horse Leopardi) was behind the bit. I think it's because it's been eight months since he last competed."

Since the Montreal Olympics, where he was a reserve rider, Winnett has mostly competed in Europe, while at the same time representing his business interests.

The riders earning 58-percent marks for the two-day competition earn the right to go to national team headquarters in Gladstone, N.J., for further evaluation.A team of six horses and six riders will then be named to compete in international events this summer.

Today's program starts at 8 a.m.