Freestate Raceway will hold Maryland's richest harness race ever Saturday with five divisions of the $320,225 Potomac for 2-year-old pacing colts. Each race is worth more than $63,000.

Hall of Fame drivers, including Billy Haughton and Stanley Dancer, will participate. Haughton has five horses entered, including Signed N Sealed, a recent 1:57 3/5 winner at the Meadowlands.

After the first 24 nights, Freestate shows a 13.1 percent upswing in attendance over last year and a 13.3 percent rise in the handle.

Jack Kent Cooke's 2-year-old filly Amdala won the fourth race at Belmont Park yesterday, an $18,000 maiden special-weight event. Amdala, trained by LeRoy Jolley and ridden by Jean Cruguet, ran the five furlongs in 58:2 and paid $4.40 to win. Amdala was sired by Foolish Pleasure.

Marine Brass, a 4-year-old colt who finished second in his last three starts, came around horses in the stretch under jockey John Adams to win the feature at Bowie in 1:23 for seven furlongs.

Hatchet Boy finished second, more than two lengths back, and Janet's Flash was third.

Marine Brass won his sixth race in 15 career starts. He is owned by Russell B. Firestone and trained by Bernie Bond.

Thoroughbred trainer Steward Mitchell seems to have the formula for winning the Primer Stakes, Saturday's feature race at Bowie. Mitchell has started seven 2-year-olds since the first race in 1975, has won four times and had one third. He will run Oxford Prince, a maiden, Saturday.

The Maryland stewards have suspended trainer Richard W. Dillon for 15 days after finding Furosemide (Lasix) in the postrace tests of his charge, Buck's Fantasy, winner of the sixth race last Saturday. Buck's Fantasy was disqualified.

Racing Commissioner William R. Goodman was sworn in Tuesday and will sit at his first meeting this month. Goodman, an attorney, replaced J. Neil McCardle on the board.