Donna Donovan, competing with three previous winners of the Potomac Plate timber steeplechase, won the 2 1/2 mile event yesterday before 9,000 spectators at Belvedere Farm.

The 8-year-old mare took the 17-jump event by two lengths, with the previous winners finishing second, fourth and fifth.

John M. Meyer's horse, turning in her most impressive performance since her flag-to-flag win in the Deep Run Hunt Cup three years ago, put rider Billy Myers into the lead for Maryland's point-to-point goal, the Governor's Cup, with her sizzling tour of the course.

"She likes to run . . . she's fast," said Myers, the 16-year-old high school junior from Upper Marlboro. "We thought about hurdles, but after today it looks like she still likes timber."

Left in the wake of the exceptional performance was Idol Fellow, which won the race in 1975 and turned in a strong run today to finish second. Third place went to Bright Tune, while last year's winner, Jay's Trouble, was fourth and the 1973 winner, Portobello III, was fifth.

The victory shot Myers into the lead for the Governor's Cup, jumping his margin over Jay Griswold to five points with only two races remaining in this spring series. Griswold's Too Far Gone was a late scratch.