The nude body of a 13-year-old West Hyattsville girl was found lying face down in the shallow water of Sligo Creek about a block from her home yesterday morning. Prince George's County police said. Authorities said the death was being investigated as a homicide.

Police found clothing belonging to the girl, Kathleen Ann Murphy, of 1709 Dayton Rd., on the bank of the creek about 20 yards away. No bruises or cuts were visible on the body, according to state medical examiner Dr. Horme Guard.

Kathy Murphy has been visiting the family of her closet friend a few blocks away until about 11:00 p.m., according to members of both families. Family members added that Kathy had been headed home when she left the home, which is about three blocks from her house.

Neither family ever reported Kathy missing. The Murphy family went to bed believing that Kathy had remained at her friend's house, and the friend's family assumed she had returned to her family's house, both families said.

The narrow creek bed where her body was found runs between a small grassy park. The Park Lawn Recreation Center, and a narrow grove of trees. The area lies on a popular shot-cut route between the street where the friend's family lives and the Murphy house in Dayton Road, the families said.

The girl's body was discovered about 9:30 yesterday morning by employes of the Washington Suburban Sanitary Commission, who were visiting the area to study the possibility of building a bridge over the creek, according to spokesman for the Maryland National Capital Park and Planning Commission, which operates Sligo Park.

Police said yesterday they had no definite suspects in the case. But investigators were probing the possible connection of the death to an incident late Tuesday night, in which a shirless youth with short blond hair was chased through the park by a neighborhood youth who said the unknown blond youth had been following a teen-aged girl.

Wayne Odham, 18, of 6802 Knollbrook, West Hyattsville, said his girlfriend was approached by the teen-aged youth about 11:30 p.m. in the park area where Kathy Murphy's body was later found. Odham, who said he had never seen the youth before, began chasing him, but was unable to find him.

Odham said he then walked up from the creek area to a parking lot behind shopping center at the intersection of Riggs Road and East-West Highway, about 50 yards from where the body was found. Two Prince George's County police cars were parked in the lot, Odham said.

Odham said he told the officers about the incident, but that "they weren't able to find anything." Police later confirmed the officers had searched the area but had discovered no traces of the unidentified youth or of Kathy Murphy.

Shortly after officers arrived at the creek yesterday morning, the girl's father, George Murphy, 53, drive past the area on Riggs Road and stopped to find out what had happened. When police told him a young girl's body had been found, he said later, he hurried home and found that Kathy was missing.

Normally, it was not unusual for Kathy Murphy to be out of the house, the Murphys said. She had spent most of the last two weeks at the home of her close friend, according to the friend's mother.

A quick call to the friend's home revealed that Kathy had left the previous evening. Kathy's mother, 51-year old Mary Murphy, had requested that she spend the night at home instead of staying with her friends, members of both families said.

George Murphy then made the long walk from the Murphy home to the creek. "All I told them," he said later, "was 'find the guy that did it.'"

Kathy Murphy was the youngest of nine children, who ranged in age from 13 to 24. Murphy, an executive assistant manager at the Hotel Washington, said Kathy, a student at Rolling Crest Junior High School, had been active in the Green Meadows-Chillum Boys Club until a little over a year ago, and had once won the club's four-sports award.

"She cared about other people," her father said. "She worked in a nursing home for a while. She had the usual interests - records, boys . . ."

Neighbors, friends, and school officials also described Kathy Murphy as a caring, friendly person.

They said that she had changed over the past year, turning from a normal, well-behaved girl with above-average intelligence to a rebellious, somewhat uncontrolled teenager who, together with the 15-year-old girl who was her close friend hung out late at night at the local shopping center, smoked cigarettes and marijuana, and flunked out of the eighth grade.

"Kathy was following [her friend]" said David W. Lindquist, a vice-principal at Rolling Crest, which enrolls about 660 students in grades seven through eight. "Kathy did well in the seventh grade, but last year, she feel in with the friend at whose house she was staying. They started getting into trouble together."

Lindquist said the two girls frequently cut classes together, were suspended once for smoking in the bathroom, and were both scheduled to repeat the eighth grade this year.

"You see this happen to kids sometimes," Lindquist said. "They'll start out well in junior high, then fall in with someone older who's been in trouble. Kathy was not a problem as far as getting along with teachers, and the kids liked her. She just got started on the problems kids have."

"They got to know each other about a year ago," said the friend's mother. "When those two were in school, if one was in trouble, the other was, too. But it was just kids mischeviousness."

"She had really changed," said Katherine Beall, who lives at 6610 Riggs Rd. opposite the rear of the Murphy house. Beall's 13-year-old daughter was also a friend of Kathy's. "We'd sometimes come home at 10 or 11 at night and see her standing around on the street corner, or dwon at the Shopping Center . . . She just came and went at night."