Fulton Wayne Smullin, 41, leading trainer-driver on the Maryland harness circuit, died last night of injuries he suffered in a ninth-race accident at Freestate Raceway Thursday night.

In a brief statement issued late last night, Prince George's General Hospital said Smullin died after his brain ceased to function because of the trauma.

Smullin's death was announced at Freestate by track president Frank DeFrancis. Standing in the winner's circle following the completion of the 11th race, DeFrancis told a crowd of 12,145 that Smullin's sister (Rita Churn) had called him to say that doctors had declared Smullin legally dead and he had been clinically dead for most of the day.

DeFrancis asked for a moment of silence. Earlier, trainer John Lare had announced that his purse winnings from last night's card would be donated to Smullin's son to help with his education. Laird had four winners at Freestate, with winnings surpassing $7,000.

Smullin suffered severe brain injuries, a fractured skull and fractured ribs in a three-horse accident. It occurred after the horse he was driving broke stride and his sulky was rammed into from behind by another horse. His horse somersaulted and Smullin became jammed against the sulky and his horse, which fell to the track.

He was rushed to Greater Laurel-Beltsville Hospital, then was transferred to the Prince George's General Hospital shock trauma unit. He had been on a life-support system.

Smullin, a resident of Seaford, Del., was the first standardbred handler to die as the result of injuries in a Maryland harness race, and the first nationally to lose his life in nearly a year. Shelly Goudreau of Canada died six days after being thrown from his sulky at Hollywood Park on Aug. 27, 1982.

Known locally as the "King of Maryland racing," Smullin had driven more than 1,500 winners for earnings of $4 million in a decade of racing. His most memorable driving performance came when he catch-drove Good To See You to third place in a heat of the 1979 Little Brown Jug.

Smullin had more than 200 winners in each of the past five years and was l2th nationally with 276 wins in 1981. A year ago, Smullin had 244 victory drives in 1,308 trips with earnings of $806,785.

This year, after recovering from a broken leg when he was kicked by a horse, he had 95 wins in 489 races with earnings of nearly $400,000.

Born in Accomac, Va., Smullin had been married twice. He leaves a son, David, 16; a brother, Frank Jr.; two sisters, Norma Jean Murray and Churn, and parents, Virginia and Frank Sr.

The last death in Maryland horse racing came in 1978, when jockey Robert Pineda was killed in a race at Pimlico. Jockey Happy Witner was killed at Timonium in the 1950's and Bernard Buddy Handford lost his life at Pimlico in 1933.