The Justice Department's juvenile delinquency branch, acting in the wake of the sexual assault of an 11-year-old boy in a D.C. courthouse cell, has raised new questions and asked for more information about how the District detains youths awaiting court processing.

Eugene L. Rhoden, specialist with the Office of Juvenile Justice and Delinquency Prevention, concluded last month in an internal memorandum that the District violated no federal statute when the youth was placed by U.S. Marshals in a D.C. Superior Court cell with three juveniles, two of whom assaulted him. But Rhoden's memorandum, a copy of which was obtained by The Washington Post, suggests that the city may have violated its statute against placing any juvenile in a facility regularly used to detain adults.

"It may well be that the District is in violation of its own statute when the city places these juveniles, for even short periods of time, in a facility that also holds adults," said Rhoden.

He has also raised concerns that the U.S. Marshals Service "around the country" may be violating laws that require the separation of juvenile and adult suspected offenders. Rhoden, whose investigation grew out of a recent House subcommittee hearing that questioned the District's juvenile detention procedures, has asked the city's Office of Criminal Justice Plans and Analysis for more information about how the District is complying with provisions of the Juvenile Justice and Delinquency Prevention Act of 1974.

The act, which was revised in 1980, is a voluntary statute that makes federal grants through the Justice Department for states that agree to work toward setting up separate incarceration and detention facilities for youths and adults. One section of the act requires keeping adults and juveniles in separate cells; another provision gives states until December 1985 to remove all children from facilities that used by house adults.

Rhoden said the District, which receives about $225,000 a year in federal grants under the act, never placed the youth with an adult and has until the end of the year to provide totally separate detention facilities. But he complained in a letter to D.C. officials that the city had never indicated in its compliance monitoring reports that it is detaining youths for brief periods in the D.C. Superior Court building.

Citing department restrictions, Rhoden declined yesterday to discuss his memorandum with a reporter. But Shirley Wilson, executive director of the city's Office of Criminal Justice Plans & Analysis, which submits the compliance reports to Rhoden, said it is the District's position that there is adequate separation of adults and juveniles.

Asked about the D.C. Superior Court cell block arrangement, Wilson said she was "not sure" if it would affect the city's compliance with the Juvenile Justice Act after the December deadline.

"It's an issue that's just been raised now," said Wilson, who argued that, because Rhoden used to head the D.C. compliance office, he was aware that the District uses D.C. Superior Court cell blocks to house juveniles temporarily. She said the recent juvenile assault case "has opened up a whole floodgate" of inquiries into city detention practices for youths.

But Gordon Raley, director of public policy for the Child Welfare League of America, said yesterday that the marshals, by using the Superior Court cell block for juveniles, "go against congressional intent, and the city is going in the opposite direction" from the federal juvenile justice act. He complained that the welfare of juveniles is being ignored while federal and city officials debate the fine points of the statute.

"They're saying that this isn't wrong just because it didn't break the law in some way," he said.