MONMOUTH, Ill. (AP) _ Police believe they have solved a 1983 double slaying with the arrest of a Peoria man who would have been 14 at the time of the crime. Authorities said more arrests are possible.

State's Attorney Greg McClintock of Warren County said Monday that the 22- year-old man's name was not released because he had been charged as a juvenile.

McClintock said he had filed a petition to transfer the case to adult criminal court.

The man is charged with two counts of first-degree murder in the slayings of Earl and Brenda Marsh, both 18, of rural Alexis. Their bodies were found in their farmhouse April 18, 1983.

The Marshes' infant son, Joshua, was left unharmed in his crib.

At a detention hearing Monday, Warren County Sheriff Gary Higbee said that the husband was shot in the chest and that Mrs. Marsh was strangled and stabbed 18 times.

Higbee testified that police believe more than one person was involved.

According to Higbee, more than one person would have been needed to overpower both adults.

McClintock said he didn't know how severe a penalty the suspect could receive if he were convicted of murder in juvenile court. But the prosecutor said he was sure the punishment would be worse in criminal court. There, the minimum sentence for first-degree murder is 20 years in prison.

Higbee said police obtained tape recordings of conversations that the suspect had about the time the Marsh couple died. On those tapes, the man allegedly said he went to a party with two other people who said they were going to rob the Marsh home.

The tapes reveal that the three drove to the Marsh home, knocked on the door and were invited in by Marsh, Higbee said. Higbee said Marsh was immediately assaulted. He gave no other details about Mrs. Marsh's death.

According to the tapes, the three then drove back to the Lake Storey area, where the suspect was let out of the car and the others drove off, Higbee said.

The man, who lived in Galesburg when the Marshes were slain, was being held without bond at the Warren County Jail in Monmouth.

Marsh's sister, Lory Olinger, 35, said members of her family were happy to learn of the arrest. But they believe others involved in the crime are still at large, she said.

The arrest ''will take some of the wondering and worrying off the family,'' she added.