The body of Gaithersburg resident Hye Ja Yi, 18, was found yesterday in a ditch at a construction site near her home, Montgomery County police reported. A state medical examiner said the teen-ager, a junior at Gaithersburg High School, had been beaten to death.

Construction workers discovered the body about 7 a.m., less than 10 hours after she was seen at Lakeforest Mall, where she worked at a store, police and a family member said.

Montgomery police Cpl. Phillip Caswell said Yi's partially clad body was found near Muddy Branch and Fields roads, about two miles from her home on West Deer Park Road.

A spokesman for the state medical examiner's office in Baltimore said Yi had been beaten on her upper body with a blunt object. There was no evidence that she had been sexually assaulted, he said.

Dennis Adams, the victim's uncle, said Yi, a native of Korea, was "a very quiet, easygoing kid. There is just no reason for this. The family has been trying to think of anyone who might do this, but there's just nothing."

Adams said the Yi family settled in Gaithersburg after immigrating from Korea in 1978, and "really have liked it here. There haven't been any problems." He said other family members told him that Yi was unable to find a ride from work Monday night.

"She was usually able to get a ride home from somebody there, but last night, she couldn't," Adams said.

Frank Masci, principal at the high school, described Yi as "a nice quiet kid and a very hard worker." He said she played the violin in the school's orchestra, and was enrolled in an academic curriculum.

Masci said he was also principal at Gaithersburg Junior High School while Yi was a student there. He recalled that she won English and math awards at the school, and continued to excel in those subjects in high school.

"She was really the type who did what she was supposed to do. This is really hard to believe," Masci said.

"She was just pretty as a picture, a sweet little girl," Hazel Peters, a neighbor of the Yi family, said yesterday. "It's just a very sad thing for everyone."

Police said they have no suspects.