When the horses left the Virginia state and county fairs 137 years ago, they went to Upperville. It is believed that the Upperville Colt and Horse Show at Grafton Farm, which opens today at 8 a.m., was the first occasion horses commanded a spotlight of their own, separate from the cows, pigs and sheep of the fairs.

Today, horses will begin strutting, prancing, running, walking and jumping for points in attempting to qualify for the Washington International and Madison Square Garden horse shows this fall. The Upperville show will run 8 a.m. to dusk each day through Sunday.

Highlights of the week include the Black Starr and Frost Three Foot Challenge event on Thursday, the $5,000 Junior/Amateur Jumper Stake and a new Family Class Saturday.

The premier event of the show will be the $40,000 Michelob/Upperville Jumper Classic Sunday at 2:30 p.m. Jumper classes are an opportunity for horse and rider to perform athletically after performing esthetically for most of the week.

In the Jumper Classic, horses will attempt to clear 12 to 15 fences ranging in height from five to seven feet. A seven-foot fence is higher than a horse's head. Those horses who jump within the allotted time without knocking any of the fences down advance to a timed round in which the fastest horse to complete the course cleanly wins.

Last year's Jumper Classic rider champion, Michael Matz of Collegeville, Pa., who won on Bon Retour, is expected to ride Sunday, but has not yet confirmed. Matz has won three Jumper Classics, twice on Bon Retour (1984, 1989) and once on Gondolier (1986).

Top confirmed performers include Joe Fargis of Southampton, N.Y., who won team and individual gold medals in the 1984 Olympics and won a team silver medal two years ago in Seoul; Barney Ward of Brewster, N.Y., Debbie Shaffner of Ambler, Pa., who is a member of the U.S. Equestrian Team; Mario DesLauriers, of Culpeper, a Canadian citizen who was a member of the fourth-place team in the '84 Olympics, and Margie Goldstein of Miami, the 1989 American Grand Prix Association rider of the year.

Also riding will be Katie Monahan Prudent of Middleburg, a three-time AGA rider of the year and a member of the 1986 world championship team. Monahan Prudent is competing again following a near-fatal accident in early spring.