The D.C. police department's youth division has tightened its procedures for detaining juveniles as a result of a case involving an 11-year-old Northwest Washington boy who was sexually assaulted in a D.C. Superior Court cell last year.

Children under 10 who have been referred to court for a serious offense will no longer be held in a Superior Court lock-up facility. Instead, a police officer must remain with a juvenile until the case is called for an initial hearing. If court is not in session, the child will be sent to the District's Receiving Home for Children.

Police are now required not to place children who are older than 10 but younger than 13 in a court cell lock-up whenever possible. Before detaining a child in this age group, police officers must consult with a police department superior about how the child is to be detained.

Superior Court rules for detaining juveniles require that a child, regardless of age, who has been charged with certain violent crimes -- including homicide, forcible rape and robbery while armed -- be detained until a judge has reviewed the case.

During the last nine months District police have arrested an average of six children a month under the age of 10 and 23 children a month who are older than 10 but younger than 13. Police Capt. David C. Bostrom, assistant commander of the youth division, said that about 30 percent of the youngsters were detained pending a court hearing.

Shirley A. Wilson, director of the District's Office of Criminal Justice Plans and Analysis, informed the City Council's Committee on the Judiciary of the new rules yesterday during a hearing on a bill that also is aimed at changing procedures concerning juveniles.

Wilson testified that having an officer remain with a child would have the effect of removing "the potential for a younger juvenile to fall prey to older juveniles while awaiting court action."

The 11-year-old District boy had no previous criminal record and was placed in a Superior Court cell block after being arrested for hitting another youth in the head with a baseball bat. While in the cell, he was attacked by 14-year-old and 17-year-old cellmates who forced him to commit sodomy. The victim later contracted syphilis.

Wilson said that the new procedures instituted by the police department should make it unnecessary for the council to adopt the legislation introduced by Council member Wilhelmina J. Rolark (D-Ward 8).

Rolark's bill would require that any child under the age of 10 in custody be taken to the court's director of social services. The director would be required to physically separate all children under the age of 13 who are detained pending a hearing from anyone older than 13 and from any child under the age of 13 who is believed to have committed a violent crime.

Rolark said she was pleased that police have new procedures but questioned whether the department is being placed in a position that amounts to baby-sitting. She said she is convinced that new legislation is needed.

Daniel N. Arshack, an attorney for the boy who was attacked and a witness at yesterday's hearing, agreed with Rolark.

Another witness said Rolark's bill is too vague to be effective. Phyllis T. Bookspan, an attorney with Georgetown University Law Center, said that it does not make it clear where juveniles would be placed after they have been separated.