Conrad Homfeld of Petersburg, Va., won the Carte Blanche World Cup today, earning 47 1/2 points on Balbuco despite failing to win any of the three main events.

Melanie Smith, 29, of Germantown, Tenn., was the leader going into the final event. But she placed 12th in it and finished second with 44 1/2 points. Smith said her horse, Calypso, a 7-year-old Dutch-bred gelding, had become skittish because of the capacity crowd in the Civic Center.

Homfeld, in seventh place entering the day, placed third in the final phase of competition, won by defending Cup champion Hugo Simon, 38, of Austria on Gladstone. Simon finished fourth overall.

Leslie Burr of Long Valley, N.J., riding Chase The Clouds, was second to Simon following a jump-off for the top spot and finished ninth overall.

Balbuco, a 15-year-old Argentenianbred bay gelding owned by Mr. and Mrs. Patrick Butler, has been Homfled's mount on the Grand Prix circuit for seven years and was the horse of the year in 1976 and 1979. They placed seventh and third in the first two phases of World Cup competition.

"I have always felt that the mark of a great horse is one that goes the distance," said Homfeld, 26, who placed 11th in the inaugural World Cup in Gotenborg, Sweden, last year. "He (Balbuco) doesn't have 900 wins (in his career) but we hang in there."

"To come so close and be beaten is a big disappointment," said Smith, the 1978 rider of the year and one of five women riders in the competition.

"He (Calypso) was more difficult to ride, especially when we jumped fences facing the crowd," Smith said. She had two knockdowns in the final jump-off.