The first championship at America's oldest horse show was awarded today to Glenmore Farm's Forge Nimbus, who won the pony breeding division of the Upperville Colt and Horse Show at Grafton Farm.

The 2-year-old Celtic Ballad out of Forge Minstral had won the pony stallion class for the Keswick, Va., stable from competing against first-and second-place winners in the division. The reserve championship went to Sprig of Mint, owned by Tammy Williamson of Southern Pines, N.C.

In the jumping competition, across the road at Salem Farm, Alan Smith of Middleburg won the intermediate jumper class on Thunder Road, owned by Twelfth of Never. Smith, one of five riders in a field of 16 to qualify for the timed jump-off, finished in 35.04.

In the first of two preliminary jumper classes, Maryann Steiert of Keswick, riding Sassakiss, edged Carl Khuen of Dickerson, Md., on Skipper in a class called touches and time. In the first round of competition the 27 entries were scored according to the number of times their horses touched the fences. Five riders qualified to compete in the final phase against the clock. Steiert finished with no faults in a time of 38.22, Khuen in 39.24.

The second class of preliminary jumpers was won by Katie Monohan of Upperville on Lord Bromont, owned by Hunterdon, Inc.