A halfway house for juvenile offenders in Lanham was closed yesterday as a result of an unsupervised weekend party there at which marijuana was used and a 15-year-old girl was beaten, Prince George's County police reported.

James Dedes, supervisor of the county's Juvenile Service Office, said the contract with Byram Homes, Inc., at 6409 Princess Garden Pkwy. has been terminated. For the last six years the facility has housed juveniles in need of constant supervision who have been referred to it by the courts.

According to Dedes, a counselor told the six youths living there Friday they could go home for the weekend.

Police and juvenile services officials said a 17-year-old from the home returned Friday night to Byram, which was then unattended, and entered the building through a window along with two girls who live in the Lanham neighborhood so they could all "smoke pot."

Police said that about 5 a.m. Monday they got a call from a neighbor who said an assult had taken place in the home.

When police arrived at the home, they said, they found "about seven" youths - including four boys who lived at the home and one of the two girls from the neighborhood - in the living room where mattresses, trash, food and marijuana pipes were strewn about.

Police said the second girl had run from the home to the neighbor's house, prompting the call to police. The girl was taken by ambulance to Prince George's General Hospital.

According to the neighbor, who asked not to be identified, the girl arrived at her front door screaming, "Help me, help me."

The neighbor said the teen-ager told her she had been beaten by two of the boys, who threatened to tie her up. "Her face was swollen, she had a lump on her ear and numerous bruises and her body," the neighbor said.

Police said the girl apparently had been beaten with a broomstick.

The girl was released from the hospital in the custody of her parents Monday, but yesterday was reported by her parents as a runaway, police said.

The four boys found at the home by police were reassigned Monday to other supervised programs run by the Juvenile Services Office, but two of them have since run away, juvenile services officials said. Two other boys who returned to their own homes for the weekend are still with their relatives, the officials said.

Youths assigned to halfway houses are not considered delinquent by the courts and cannot be physically detained at a state facility. According to files on the youths involved in the weekend incident, charges against them ranged from robbery to possession of a deadly weapon.

Officials of neither the Juvenile Services Office nor Byram Homes Inc. could explain why the home was left unattended over the weekend.

The state was paying Byram $660 a month for each juvenile in its care. In addition, the county gave the home an annual grant of $20,000.

Residents of the Lanham neighborhood formed a committee a few years ago to oppose the presence of the home, which they claimed generated vandalism.

The county has two other halfway houses for juveniles, one in Bowie and one in Glenn Dale.