A court-appointed monitor is investigating three incidents of alleged staff beatings of youths placed at the District's juvenile detention facilities in Laurel, including one case in which a youth apparently was knocked unconscious briefly and did not receive medical attention for two days.

In one of the incidents, the acting school principal at Oak Hill is under investigation by the U.S. attorney's office in Baltimore for allegedly striking a youth who was being restrained by several counselors. In another case, involving a youth and a staff counselor, a witness said he lied to police about who initiated an altercation.

Youth Services Administrator Jesse Williams acknowledged yesterday that beatings had occurred, but said that an internal investigation revealed that two of the cases involved a justifiable use of force. He declined to comment on the school principal case because of the pending federal investigation.

"As far as we're concerned these cases are not closed regardless of what the system says about them," said Michael Lewis, appointed last year by a D.C. Superior Court judge to oversee implementation of a court-approved consent decree. "A juvenile institution must be operated lawfully and if kids are being beaten that is just unlawful and intolerable."

In another development, oversight hearings on Oak Hill are scheduled to begin today before D.C. Council member H.R. Crawford (D-Ward 7), who has asked Youth Services Administration officials to explain recent reports that about 25 percent of the youths assigned to Oak Hill, the maximum security facility, are missing and listed as escapees.

An internal report prepared by Department of Human Services officials show that at least 141 youths have escaped from Oak Hill since the beginning of the year with nearly 40 percent of those who have escaped still at large.

The three alleged assaults under investigation have been the subject of a series of complaints by the youths' lawyers to the monitor, judges and police. In two of the cases, the youths were transferred by a D.C. Superior Court judge to another institution.

In one incident, a former counselor at Oak Hill and its annex said in a series of interviews with The Washington Post that he lied when a U.S. Park Police detective questioned him about a July 4 assault involving a student locked in his room at the annex, formerly known as Cedar Knoll. Roderick Yarbrough, who was fired at the end of July, said he told the detective that a scuffle broke out between the youth and another counselor after the youth rushed the counselor and provoked the fight.

U.S. Park Police sources said yesterday that Yarbrough's testimony was crucial in the decision made by the U.S. attorney's office not to prosecute the other counselor.

"He was the only independent observer who was not involved," said one source.

According to Yarbrough, a former substitute teacher for the D.C. public schools, "the boy was beat up bad . . . but I lied and told him {an investigator} the kid started it. I was still there and I had to protect myself and my job."

Yarbrough said he was fired from his job after another counselor alleged that he drew a knife on some students in the hall, an account that Yarbrough denied. Sources who have seen an internal report on the alleged incident said yesterday that other students also claimed to have seen the knife, but said they did not believe Yarbrough was being serious.

According to Yarbrough, who was in the locked dormitory at the time of the July 4 assault, the alleged beating occurred after the boy repeatedly banged on his locked door and shouted to use the telephone. The youth had been told earlier in the morning that his grandmother had died and he wanted to use the phone again after unsuccessful attempts to reach his mother.

Yarbrough said the counselor finally opened up the boy's door, exchanged words with him and then grabbed the youth, threw him to the ground and kicked and hit the youth in the face until the boy lay unconscious on the floor.

He said the boy "never raised his hand to beat {the counselor} and never raised his hand to swing back."

The youth suffered a black eye in the assault and woke up vomiting after a period of unconsciousness, according to the youth and his lawyer, but did not receive medical attention until two days later when the youth called his lawyer to tell her what happened.

Yarbrough's latest account coincides with those given by the 16-year-old to police and to The Washington Post.

In the case involving the school principal under investigation by federal prosecutors, internal reports show that after a scuffle with another staff member on May 7 a youth spat on the principal and the principal began hitting the youth, who had been restrained in the school hall by several other counselors.

The reports show that other staff members and students then tried to restrain the principal.

The principal declined to comment yesterday.

The third incident involves four youths at the annex who said they were repeatedly punched and kicked by staff members on June 16 after an unsuccessful escape attempt in which they threw a cup of ammonia in a counselor's face.