The Maryland Court of Special Appeals ruled yesterday that Montgomery County police violated the rights of a 10-year-old Aspen Hill boy when questioning him last summer about the July 19 assault on his 7-year-old playmate, Steven Wilson Jr.

In a 10-page opinion written by Judge C.J. Gilbert, the state's second-highest court reversed a ruling by Montgomery County District Court that the 10-year-old was delinquent, and sent the case back to the District Court for a new trial.

Attorney Arthur G. House, who represented the 10-year-old, said he will recommend that the case be dismissed.

Montgomery County Police spokesman Sgt. Harry Geehreng said officials will confer with Montgomery County State's Attorney Andrew Sonner to decide how to proceed in the case.

The 10-year-old was committed to a state juvenile training facility Oct. 18 after he was found delinquent on charges of assault with intent to maim, assault and battery and making a false statement to police in the incident, which occurred in an area near Turkey Branch Creek.

After the incident, the 10-year-old told police that he and Steven had been approached by two teen-agers carrying fold-up knives. The 10-year-old said he had escaped but that Steven had fallen down a steep embankment and been assaulted by the older boys.

Steven suffered multiple facial cuts and head injuries in the attack.

Four days after the incident, the 10-year-old ran away from home. Police found him in a nearby neighborhood and took him to the Wheaton Police Station where he was questioned -- alone -- and charged.

Yesterday's court ruling held that the statement that the 10-year-old made to police should have been suppressed at the delinquency hearing because he had been deprived of his rights under the Miranda ruling.

" . . . The record shows a 10-year-old child, with no more than a fourth grade education . . . was picked up as a runaway," the ruling said. "He was transported to a police station where he was interrogated for several hours by detectives. He was not informed that he was free to leave the station, nor was he told that his mother was in the stationhouse waiting room. Moreover, there was testimony from a detective which explicitly said that the boy was in 'police custody.' We are led to the conclusion, therefore, that the boy reasonably perceived himself to be in the custody of the police."

The court also said that even though the 10-year-old technically had waived his Miranda rights, the waiver "was almost, if not totally meaningless" because of his age and because he had not had any counseling or guidance from a parent or guardian prior to waiving his constitutional rights.