A last-minute surge of energy carried Grey Chief and U.S. Equestrian Team member Katie Monahan to victory in the $7,500 International-Open Jumper Class at the Washington International Horse Show at Capital Centre last night.

Monahan, 28, of Upperville, Va., pushed the 13-year-old gray gelding to victory in a photo-finish over Switzerland's Silverbird III and Walter Gabauthuler, also 28. Grey Chief and Silverbird III returned to the course where each jumped five-obstacle courses simultaneously. There had been 20 horses in the starting field.

Frederick Cottier of France rode Fidelite A to tie with Hugh Mutch of Middleburg, Va., aboard Thunder Road. The United States has 85 points in team competition, followed by Switzerland with 38, France with 20 and Canada 18.

In afternoon competition, Joyce Park skillfully guided Rocky, a 9-year-old gelding, to victory in the $2,000 Owner Jumper Classic and the Amateur-Owner Jumper Championship with 12 points. The bay, owned by John W. Hamilton of Jefferson, Ohio, outlasted 18 other entries.

Have At It, a 10-year-old gray gelding owned and ridden by Maggie Moss Flynn of Greenwich, Conn., was second, followed by Adam with Lisa Tarnopol in the saddle for third. Kevin Maloney, 28, of Warrenton, Va., was fourth on his Boing. The Woodsman, an aged bay gelding, was named reserve champion.

In the Jack Russell terrier races, Lucy, owned by Holly Woodburg of Vienna, maintained her winning record when she withstood a field of 18 and three demanding heats to be named champion. Paddy, owned by Dr. Marilyn McKay of Monkton, Md., was second, followed by Toffee, owned by Liz Dunning of Boyce, Va. Rocky, previously unbeaten in the week-long competition, was fourth.