An 11-year-old Northwest boy who said he was just horsing around when he hit a playmate on the head with a baseball bat was charged with assault and locked in a cell at D.C. Superior Court, where he was beaten and sexually assaulted by two older boys. He was later found to have contracted syphilis.

After the May 23 incident, the boy -- who had never been in trouble with the law and previously had undergone psychiatric treatment for depression -- became suicidal and was placed in the care of physicians at Children's Hospital, who continue to treat him.

Two youths with several previous criminal convictions, one aged 14 and the other 17, have pleaded guilty to two felony counts of sodomy for their involvement in the attack on the five-foot, 90-pound boy, according to the D.C. corporation counsel. They are being held in the city's juvenile detention facility in suburban Maryland.

The felony assault charge against the boy was dropped three weeks after his arrest, without objection from city prosecutors. And, in the opinion of social workers who interviewed him at the time of the incident, the charge should never have been leveled.

Relatives of the boy, who is now 12, have informed the Justice Department of their intention to sue the U.S. Marshals Service, which operates the courthouse cellblock, for $1 million, claiming that deputy marshals should have protected him. And they have criticized police handling of the incident, saying they do not understand why the boy was arrested and jailed.

Experts in juvenile justice question the use of police authority in the episode, described by social workers as an accident typical of playground horseplay. The boy said he and his friend were testing the strength of their plastic batting helmets when he swung the bat too hard and his friend turned his head the wrong way.

The friend, who was treated at a hospital for a deep cut on his head, and his mother complained to police. City social workers at the time of the arrest recommended that the charge be dropped, and city prosecutors paused before pressing ahead with the case against the boy; they did not file the assault charge in court until June 1, days after they learned that he had been attacked in the cell.

Psychiatrists involved described the incident as a major psychological blow to a child who had already suffered numerous traumas. He had earlier been hospitalized for depression when his stepfather left home. One month before his arrest, a close friend had hanged himself. And four months after he was attacked in the cell, his mother died of acute pancreatitis.

"It is inconceivable that one youngster of his age should be subjected to the myriad of psychological assaults that this youngster has had to face," said psychiatrist Bruce Copeland, who evaluated the boy, in a letter to the family's attorney.

The boy and his grandparents remain bitter over his treatment by the city's justice system.

"I think it was rotten as hell," said the grandfather, a retired D.C. government employe. "I never thought they would put him in a cell like that. It's not right to treat a little kid like that."

"If I ever see one of those boys from the cell again, I'll get a gun and blow their head off," the boy said.

Officials in the Marshals Service will say only that they have investigated the incident and will send a report to the Justice Department.

"We have no comment on whether it did or didn't happen," said Gerald Auerbach, the service's general counsel. "The matter is going to be resolved in court sooner or later . . . . We have nothing more to say."

City records on juveniles are confidential by law, and the boy and his family agreed to be interviewed only on condition that their names not be used.

Copies of the police, court and hospital records obtained by The Washington Post detail events leading to the boy's arrest, his incarceration and his treatment following the attack. Some specifics were confirmed by a spokeswoman for Mayor Marion Barry. Playing in Parking Lot

On May 22, the boy, his friend and a girl were playing in the parking lot of Nativity Church at 6000 Georgia Ave. NW. The 11-year-old said his friend bounced a softball off his helmet to see if it worked. He said he wanted to use his baseball bat to test the helmet his friend was wearing.

"I said, 'Let me hit you back,' " the boy said. "He said, 'Alright.' I wasn't going to hit him hard. I was just going to tap him like he did me with the ball. I was trying to hit the helmet and he ducked.

"I knew this boy for a whole lot of years," the boy said. "I was like a best friend of his."

The bat missed the helmet and struck the other boy on the back of the head, and he ran home bleeding, the 11-year-old said. An ambulance was summoned and the injured boy was taken to Children's Hospital, where doctors closed the wound with eight stitches inside the cut and four outside, according to a police report.

Later that evening, the injured boy and his mother, Carolyn Reed, walked to the friend's house and Reed asked how the other family planned to pay for the hospital bill.

The mother of the 11-year-old, a sales clerk at a local department store, "said she wasn't paying for nothing because she didn't have no money," according to the grandfather. Reed "said she was going to put him in jail," he said.

"They were friends, yes," said Reed, who reluctantly answered only a few questions about the incident. "They may play together. But he assaulted my son. He almost killed my son. If it hadn't been for that helmet, he would be dead."

The following morning, according to police records, Reed took her son to 4th District police headquarters and filed a formal complaint against the other boy.

"Complainant reports . . . that while on the Nativity school playground . . . he was struck about his head with a baseball bat held in the hands of the above-described subject without provocation," the complaint said.

The arrest report form subsequently filed by Officer Bettie J. Eppes of the 4th District youth services branch added that the injured boy said that "he was playing with his friend when his friend hit him in the head with a baseball bat. The boy went home and advised his mother what had happen ed ." Custody Order Prepared

Later, Eppes called the 11-year-old's mother at work and told her a custody order "was being prepared for her son's arrest," according to police records.

The following morning, May 24, the mother brought her son to the station house, where the boy "was advised of his rights" and gave a statement.

"We were coming up the street and I had the baseball helmet on . . . and I told the friend to hit me with the ball to see if it hurt. He hit me real soft," said the 11-year-old, according to Eppes' report.

"Then we went to Nativity and the girl playmate came up and I was playing with her, making like I was going to hit her. Then I started playing with the friend . He had a helmet on. I swung at him, but before I could stop, I accidentally hit him."

Eppes charged the boy with assault with a dangerous weapon, a baseball bat. The boy said he was escorted to a police cruiser and driven to court while his grandfather and mother followed in the family car.

"Each case has its own merits," said Sgt. Edward Synan, the supervisor who signed Eppe's arrest report, when asked to explain why the boy was charged. "There might have been some circumstantial evidence.

"Depending on the officers' judgment on what would be the best alternative, they might release him as just a neighborhood scuffle," Synan said. "They might consider more drastic means. What we try to do is keep kids from coming back."

A second supervisor involved in the case, Sgt. Barry A. Thornes, said, "The complaint is ADW, baseball bat. That's a felony." Pressed to explain, he said, "I can't talk about it. It's a juvenile matter." 'Only [to] Scare Him'

In a court motion seeking to dismiss the assault case, the family's attorney, Daniel Arshack, quoted the mother as saying that police officers told her they were taking her son downtown but would "only scare him a little" and release him. The boy, in an interview, insisted that police told his mother "that they wouldn't put me in no cell."

Once at the courthouse, police turned the boy over to deputy U.S. marshals around 10:30, pending a court hearing on the felony charge, police sources said. Deputies placed him with three other boys in a cell reserved for juveniles.

Kathy Williams, spokeswoman for Mayor Barry, said the oldest boy, 17, was being held on charges of burglary and auto theft. A 14-year-old was waiting to appear in court on a charge of assault with a dangerous weapon.

While the boy's mother waited upstairs in the office of the court's social services branch, a social worker interviewed her son. The interview became the basis for a recommendation that no charge against the boy should be brought in court.

"Despite seriousness of injury, this did not necessarily occur through a malicious intent to harm complainant," said a report signed by social worker Michele Hunt, "but rather because of the playful antics of a 11 -year-old."

Hunt noted the boy's "stable home adjustment" and "satisfactory school adjustment" and said that the two boys "have been longtime friends."

Nevertheless, the D.C. corporation counsel, which prosecutes juvenile offenders, signed a petition charging the boy with assault. "It was a serious injury," Williams said. "They city prosecutors felt this was a serious case."

Sources said that sometime before lunch, while the paper work in the case was being completed, the boy was attacked by his 14-year-old and 17-year-old cellmates.

The older youth "called me over by the toilet and told me to start doing that stuff," the boy said. "I said, you must be crazy. I walked away and they started beating me up. They started beating me and kicking me." He was forced to commit sodomy.

Later, the boy said, a deputy marshal served lunch, but the boy refused to eat and said nothing about the incident.

"He was scared. He had been threatened," said one detective who investigated the assault. "He was told that he would be beaten again if he opened his mouth." Assaulted a Second Time

After lunch, the boy said he was again assaulted by the two older youths and again was forced to commit sodomy. Court records show that, like other prisoners, he was later asked to give a urine sample to test for drug use, which proved negative.

Citing the pending litigation, a spokesman for the Marshals Service refused to discuss its policies for placing youths charged with varying offenses in cells or how the cellblock is monitored.

Sometime around noon, the boy was released to his mother, a detective said. He had never been provided with an attorney and had never appeared in court. The petition signed by the corporation counsel was not filed.

The boy said he told no one about the attack until that evening, when he spoke to his aunt about it. She told his mother, who called police the following morning.

Detectives in the police sex offense branch said they picked the boy up at his house and drove him back to the courthouse, where he showed them the cell in which he had been attacked.

Police then drove him to Children's Hospital for treatment and eventually tracked down the fourth boy who had been in the cell -- a 12-year-old -- who corroborated the story, sources said.

"There was no doubt as to the veracity of the victim," said one police official involved.

Williams said prosecutors learned of the attack in the cell around May 28.

On June 1, they filed the assault petition against the 11-year-old in court and he appeared before Judge Nicholas S. Nunzio with attorney Arshack.

Nunzio ordered the boy released pending another hearing, and later, on June 14, the judge dismissed the case "for social reasons," without objection from the government. Williams said prosecutors dropped the case because the boy "was now a witness" in the sexual assault.

"It's always a matter of weighing the one against the other," she said.

According to Arshack's motion to dismiss the charge, the city "has brought more retribution and punishment upon the boy already than could possibly be levied through these proceedings."

But the incident in the cellblock was only beginning to take its toll.

The boy started wetting his bed and fell into "frequent crying spells," according to a report by physicians at Children's Hospital. He had trouble sleeping and began sleepwalking. His work in school dropped off.

"He talked about hurting himself," said psychiatrist Copeland in his report, "and noted that everyone would be just better off if he weren't around."

On July 10, the mother admitted her son to Children's Hospital and it was determined that he had syphilis of the mouth. He remained at the hospital for more than six weeks, the second time in a year that he had been taken there because of recurring bouts of depression that had begun when he was 10. He asked nurses whether he would have problems relating to females when he got older.

"What is clear is that this was a highly vulnerable child to begin with," Copeland wrote Arshack. "Basically, this is a child with rather limited psychological resources for whom a stress of the magnitude here . . . would be likely to have rather profound effects."

Copeland said that the boy "will need rather intensive psychiatric follow-up for years to come, and even so, there are no guarantees about the eventual success of this endeavor."

David Lloyd, legal counsel for the child protection unit at the hospital, said syphilis, if properly treated, "is considered cured . . . . "

In September, the boy's mother died of a bleeding pancreas, perhaps, Arshack said, the result of mixing drugs she had been taking for her own depression. 2 Attackers Plead Guilty

The two youths who attacked the boy pleaded guilty to sodomy charges Sept. 17.

Reed, the mother who filed the original assault complaint, expressed no surprise that the boy who struck her son with a baseball bat had been attacked in his cell. But she said she was shocked that the charge against him had been dropped.

"I had no idea it was dismissed. We never even went to court about it," she said. "I'm glad to know that, because I just got another hospital bill for $88."

"It's tragic what happened to this child," said attorney Donna Wulkan, one of the city's leading advocates on children's rights. "There certainly should have been significant monitoring in the cellblock to prevent things like this happening. And perhaps there should have been some screening to be sure that this child, who is a minor offender, was not mixed with more serious offenders."