A letter writer who claims to be the city's child-killer has raised the threat of possible violence against more children at a Sammy Davis-Frank Sinatra benefit scheduled here Tuesday night.

The concert is designed to raise more than $100,000 to further the investigation of the slayings of 20 black children here over the last 20 months. One child remains missing. The body of the 20th victim, Curtis Walker, 13, who disappeared 16 days ago, was found floating in a river in a southeast Atlanta suburb Friday.

A portion of the letter -- one of two received by local newspapers last month and turned over to police -- was published in the combined Sunday editions of The Atlanta Journal and Constitution. In it, the writer rails against the concert and raises this threat: "Consider . . . while everybody's watching Sammy and Frank, who'll be watching the children . . . ?"

Members of the special task force investigating the baffling child murders and disappearances are still debating the authenticity of the letters, sources say, but police are giving them more than routine consideration, according to the newspaper. Neither was published previously at the request of police, who in meetings with editors protested the newspapers' decision to publish even one sentence from the letters.

However, because one of the letters contained what could be construed as at least a veiled threat to murder another child during a specific time frame, the newspapers decided to release some details, Jim Minter, vice president and executive editor of the newspapers, said today.

"We have no way of knowing whether the letters are authentic," said Minter. "We are not policemen. We turned them over to the police, and we withheld information at the request of police.

"However, because one sentence in the second letter can be interpreted as a threat, we sincerely believed we must report it. We did not reach this decision lightly."

The newspapers continue to withhold other details, because police have expressed fears that publishing the information might compromise the investigation. "We have cooperated with the police and will continue to cooperate on matters involving the investigation," said Minter.

Police have received a number of letters and phone calls from persons claiming to be the killer or killers. Several have been traced and found to be phony. Police believe others are from cranks. But authorities say they are still examining with diligence the letters mailed to the newspapers.

The letter from which the quote was taken was written to Richard Matthews, a columnist for the Journal, soon after he wrote a compassionate Feb. 17 column about the inner turmoil of a child-killer he once covered as a reporter.

"It was shattering to him to realize what he had done, because he never meant to kill youngsters," Matthews wrote in the column some editors believe invited the correspondence."Perhaps Atlanta's killer feels that some way -- loving the children he picks up but unable to control whatever force is pulling his strings and making him murder them. Perhaps some part of him wants badly to surrender, to cut those strings, but he is trapped between fear of the puppeteer that controls him and fear of the angry reaction that might await him if he did give up."

Atlanta Public Safety Commissioner Lee Brown expressed concern in meetings with the editors that publishing such a warning might, in effect, dare the killer or a copycat killer to attack a child Tuesday night.

"We were deeply concerned over such an implication, but felt we had a moral and journalistic obligation to satisfy the public's right to know," said one editor who sat in on one meeting with police. The letters not only contained information published or broadcast by the news media, but some details that police could use to enlighten them about the individual and ultimately tie the writer to the killings, said the editor.

As the newspapers' front page story on the letter hit the stands this afternoon, more than a dozen police officers stalked the banks of the South River, where the partly clothed body of Curtis Walker was discovered. A helicopter whirred overhead and a boat with investigators floated in the green murky water looking for clues. "We're looking for anything, anything that looks useful . . . like clothing he might have had on at the time of his disappearance," said one officer.

Across town from the police search, about 400 volunteers gathered at the West Hunter Street Baptist Church in downtown, divided into two groups and began searching wooded area in abandoned buildings in at least three Atlanta neighborhoods. The volunteers, joining together in the 21st weekend search, were hunting any evidence that might help the special police task force. The disappearance of 16-year-old Joseph Bell, last seen Monday morning, has not yet been turned over to the task force.

An autopsy performed today confirmed that Walker died from asphyxiation. But De Dalb County medical examiner Joe Burton declined to say whether the child was strangled or suffocated. The body was badly decomposed, contrary to earlier reports, and is believed to have been floating in the river for two weeks.

Crowds of children that usually bound gleefully about at the Bowen public housing project, where Walker lived, were nowhere in sight today, aftern ews of his murder spread. Inside the two-bedroom apartment where he lived with three brothers, Walker's mother, Katherine Leach, declined to talk to reporters. She was taking it "very badly," said her sister, Odessa Tate.