The French Equestrian Team had four quick, perfect rides in a shortened jumpoff round to win the Bank of Montreal Nations' Cup at the Washington International Horse Show last night at Capital Centre.

France defeated the United States and Britain, respectively, in the tiebreaker. Canada finished fourth. Team members each completed two identical rounds in the event. The top three teams were tied after those rounds and advanced to a jumpoff.

The best three of four scores in each of the first two rounds counted for each team. Scores are based on penalties incurred for fence knockdowns and for failure to finish within the allotted time.

The United States and Britain each finished the first round without knocking down a fence, entering the second round with the advantage over France (four faults) and Canada (20 faults). The two leading teams had four faults each in the second round and France had none to create a three-way tie. The tie-breaking round was a six-fence jumpoff, timed in case of another tie.

The team for France, including Philipe Rozier, riding Malesan Oscar Minotiere, Henri Prudent on The King, Jeanp-Marc Nicolas on Midway Saint Paer and Herve Godignon on Moet et Chandon Quidam, had the fastest time in the jumpoff with 99.27 seconds.

For the U.S. team, David Raposa, of Clinton, N.Y., riding Seven Wonder, and Alice Debany of North Salem, N.Y., riding The Natural, each finished both rounds and the jumpoff without any penalties. Tony Font of Houston received eight faults on Lego after completing the first round cleanly.

Hap Hansen of Encinitas, Calif., did not need to ride in the first round since his teammates had three perfect scores. In the second round Hansen and Zulu needed a perfect ride for his team to win. When Zulu tipped the 10th fence, it fell for four faults, creating the tie. Hansen had four faults in the jumpoff, but that team score was dropped.

The United States had three clean rounds in the jumpoff but was slower overall in 1:01.37. Britain, with Tim Grubb and Ever, Joe Turi and Waysider, Nigel Coupe and Invisible Lad and Michael Whitaker and Henderson Gipflsteurmer, also had three faultless rides, but finished third (1:03.38).

Debany is the leading international rider with 10 points, Hansen is second with seven.

Earlier, Todd Minikus of Lake Forest, Ill., rode Thrilling through two faultless rounds to win the $7,500 National Open Jumper competition and the O'Meara Trophy. It was the second open jumper victory at the show for the horse and rider. Last night they defeated the field of 16 competitors, finishing the jumpoff fastest in 31.826 seconds.