The mutilated body of a 5-year-old boy whose head had been cut off was found yesterday evening on a love seat in the living room of a second floor apartment in the Adelphi section of Prince George's County.

Describing the bizarre incident as baffling, veteran county police spokesman Robert Law said the decapitation, which is being investigated as a homicide, was without precedent in the county in his memory.

In addition to the head, the boy's arms were cut off. The head and arms were found near the body of the boy in the University Garden Apartments, 7960 18th Ave., about one-quarter mile north of Riggs Road and University Boulevard.

No positive identification of the victim had been made by late last night. Law said investigators had determined no motive and had no suspects.

"It's unbelievable," one police official said of the discovery, which came shortly after 5 p.m. "It's a very ugly scene."

According to the spokesman, authorities learned of the incident in a call "from a very, very hysterical lady."

The caller was believed to be the child's aunt, according to Law, but no identification was released.

Law said the woman who discovered the body was believed to be the sister of the child's mother, who had not been located by police.

According to Law, the caller had a key to the apartment and was going there yesterday evening to visit her sister when she found the body.

Investigators continued checking the apartment hours after the body was found.

The woman who discovered the body, and several persons who lived near the apartment, were being interviewed by investigators late last night.

"We're looking for anything to help unravel what's gone on here," said Law. "We know we have a decapitated young child, and that's it."

The inability of police to find the child's mother or to make a positive identification impeded their investigation, he said.

"It's baffling," he said. The spokesman said he did not know what had been used to sever the boy's head and arms.

Neighbors said police had been called Saturday to the apartment where the body was found. Police declined to confirm or deny the report.

Blood found in the apartment was dry. The child's body was to be taken to the state medical examiner's office for an autopsy to help determine the time of death, Law said.

From outside the apartment, a Christmas tree, adorned only by a star mounted at the top, was visible through the uncurtained living room window. A vase holding two or three flowers could be seen on a shelf, and a photograph that appeared to show a young woman in academic or church robes rested on another shelf. A program from a recent church service was found in the apartment. A child's bicycle was on the balcony.

Of neighbors reached last night, none knew anything about the apartment's occupants.

One neighbor said there seemed to be little mingling within the complex, which provided considerable anonymity to its residents, who she said included a high proportion of recent immigrants and college students.

The apartment development, described by one resident as often noisy with the sounds of children playing, is about one-half mile east of the Langley Park shopping center and one mile west of the University of Maryland campus.

Neighbors and police indicated a belief that there had been a number of violent incidents in the general area during the past year or two.

"But this is really terrible," said one resident of the apartment complex.