One of two 10-year-old Arlington boys charged with felonies for allegedly putting soap in their teacher's drinking water has pleaded guilty to a reduced charge, law enforcement sources said yesterday.

The Randolph Elementary School fifth-grader pleaded guilty to misdemeanor assault and battery on Monday in Arlington Juvenile and Domestic Relations Court and is scheduled to be sentenced next month, the sources said.

Because the juvenile judge has ordered the attorneys and the boys' families not to discuss the case with the news media, Arlington Deputy Commonwealth's Attorney Theo Stamos said she could not comment yesterday. The boy's defense attorney, Richard McCue, did not return telephone calls.

Juvenile judges have wide discretion in sentencing, and the sentence in a misdemeanor assault case could include probation or counseling. It is unlikely that the boy would be sentenced to a detention facility.

Patrick N. Anderson, who is representing the other 10-year-old boy, said his client is scheduled for a court hearing Jan. 10 but declined to comment further.

Both boys were originally charged with trying to kill or injure their teacher by "adulterating" his drinking water, a felony.

The case has attracted national attention, with some parents and educators saying that the teacher, Michael D. Searles, overreacted by pursuing criminal charges. Searles was not injured, and school officials had already suspended the boys for the Oct. 12 incident and ordered them to perform community service.

Both boys are Hispanic, and Hispanic parents organized a protest rally outside the Arlington courthouse earlier this month.

Police Chief Edward A. Flynn said yesterday that the judge's gag order, while protecting the best interests of the children, has prevented police and prosecutors from talking about the allegations.

"It has been frustrating to listen to people who know nothing about the specifics of this case or the context of this behavior attacking the victim for trying to help these kids," Flynn said.

Police have said the soap was an alcohol-based antibacterial solution that was squirted in the teacher's water bottle. A law enforcement source said police investigating the incident were told by other students that the two boys had made threats against their teacher and had plotted to harm him.

Before the gag order, the boy who is scheduled for a court hearing next month had said in an interview that it was the other boy who squirted the soap in the water bottle. He said the boy did it because he didn't like his teacher, who often sent him to the office.