Pico, an aged chestnut gelding, jumped the 7-feet-3 3/4-inch wall last night to win the $10,000 puissance, the featured jumping event at the Washington International Horse Show, before a crowd of 10,999 at Capital Centre.

"He tries to please me. All year he's been my No. 1 horse and he really isn't a No. 1 horse," said rider Barney Ward after his mount returned to a fifth round of power jumping to win the class. "But he has really held his own. I can't compete a lot with him. Tonight could have taken a lot out of him. It could have taken the peak out of him."

Pico began the evening showing third in an original class of nine starters with the wall set at 5-9. The class was possibly the smallest puissance field in 26 years of the Washington show, and dwindled to three horses jumping a 7-3 3/4 wall by the fifth round.

Victory at the wall did not come easy to Pico or to the former semiprofessional football punt returner-turned-show rider. Pico bobbled over the third-round, 6-9 1/4 wall, sending horse and rider tumbling into the dirt.

"He's so powerful behind that a lot of times his rear end overwhelms his front end," Ward said. "He pushed too far and too strongly and he did just like a cartwheel. He's done it once before in New York when he won the puissance last year."

Ward, from Brewster, N.Y., who set the North American indoor high jump record at 7-6 3/4 at the 1982 Washington show aboard Glandor Akai, did not attempt to break Sweet 'n' Low's 7-7 1/2 record set here last year.

Big Bird, ridden by Doug Henry, crunched the final-round wall, but finished second. Third-place Crocodile, with Henri Prudent in the saddle, refused the jump.

Wellington, ridden by Hugh Graham, finished fourth, while Rio, ridden by George Morris of Pittstown, N.J., and U.S. equestrian team member Melanie Smith, aboard Potluck, tied for fifth place after retiring at the end of three rounds.

The U.S. team continues to lead in the international riding standings with 53 points, Great Britain has 29, Canada 25. U.S. rider Leslie Burr is the leading international rider with 16 points, followed by Englishman Robert Smith with 10.

The eight-day show winds up Sunday with the $35,000 President's Cup Grand Prix.

Jazzote, a quarter-horse gelding owned and shown by George Glover of Bay City, Tex., won the non-pro championship cutting class. Peppy's Paddock, owned and shown by Ken Welch of Middlebrook, Va., finished second. Triangle Gold War and War China, owned and shown by Gilbert L. Porter, Sandy Spring, Md., tied for third.