Forestville High School football star running back Rico Leroy Marshall died of an overdose of cocaine, Maryland's chief medical examiner said yesterday.

"We feel that he had an excessive amount of cocaine in his blood," said Dr. John E. Smialek, the medical examiner, who was attending a conference of the American Academy of Forensic Sciences in Philadelphia. "There was evidence he'd ingested it."

Prince George's County police had said they believe the 18-year-old athlete swallowed six small chunks of crack, a concentrated cocaine derivative, to avoid arrest when he was approached by officers about 1:30 a.m. Saturday in a heavily traveled drug-selling area along Nova Avenue in Capitol Heights.

Marshall's father, Leroy Marshall, reiterated yesterday the contention of family and friends that the younger Marshall was not involved in narcotics. He also questioned the medical examiner's report.

"I suspect there's been some foul play," Marshall said in a telephone interview from the family's Glenarden apartment. He declined to elaborate.

Smialek said toxicology results received Sunday indicated that Marshall, who rushed for 1,026 yards last year and had accepted a scholarship offer to play football next year for the University of South Carolina, had 4.5 micrograms of cocaine per liter of blood.

The autopsy performed Saturday also revealed cocaine in Marshall's stomach, Smialek said.

He said there was no way to tell after the cocaine dissolves in the system "whether it's crack or cocaine."

Smialek said such large amounts of cocaine stimulate the nervous system and can cause cardiac arrest. "It's pretty clear as to the cause of death," he said of the apparent drug overdose.

Further tests being conducted on Marshall's heart may establish when the drug was ingested and whether he had used drugs in the past.

Smialek performed the autopsy on Len Bias, the University of Maryland basketball star who died of cocaine intoxication June 19, 1986. Bias had 6 micrograms of cocaine per liter of his blood, that autopsy revealed.

Prince George's County police, besides detailing their encounter with Marshall in Capitol Heights on Saturday, reported that Marshall had been arrested Dec. 22 in the 1400 block of Nova Avenue, and had been accused of possessing 66 plastic bags containing cocaine.

Marshall's family and friends have said the teen-ager was not involved in narcotics trafficking and have said the family was unaware that he had been stopped and charged as a juvenile. He turned 18 last week.

County police officials said yesterday that Marshall was released to his parents' custody after his arrest as a juvenile.

Police said Carolyn Marshall, the teen-ager's mother, signed a release document at 11:20 p.m. on Dec. 22. A police official said parents must prove their identities before signing release forms.

"My wife and I don't have any idea about that," Leroy Marshall said before his son's wake last night. "She didn't sign anything. They {police} haven't given me any information."

In the aftermath of Marshall's cocaine-induced death, several members of the Prince George's school board said yesterday that school officials might have intervened to help the high school senior if they had known he had been arrested in December.

Board member Angelo Castelli said he and others plan to urge Maryland legislators to amend a state law that forbids law enforcement agencies to notify school officials when students are arrested.

"I would like to see at least principals, vice principals of high schools, even middle schools, be made aware that we have someone who needs special attention," Castelli said.

"I think it's a shame that we don't have the ability to know these kids are getting into trouble."

Prince George's school spokesman Brian J. Porter said Superintendent John A. Murphy supports increased cooperation between agencies in dealing with drugs and discipline.

Staff writer Jeffrey Yorke contributed to this report.