One of two Arlington 10-year-olds charged with putting antibacterial soap in their teacher's drinking water was sentenced yesterday to probation and counseling during a closed hearing in Juvenile Court, according to a source close to the case.

The Randolph Elementary School fifth-grader pleaded guilty last month to a reduced charge of misdemeanor assault and battery. Both boys originally were charged with felonies for allegedly trying to kill or injure their teacher by "adulterating" his drinking water.

Both the prosecutor, Assistant Commonwealth's Attorney Anthony P. Hudgins, and Richard J. McCue, the boy's attorney, said they could not comment because they are still covered by the judge's gag order. Juvenile Court Judge Esther Wiggins closed all hearings in both cases and ordered the attorneys not to discuss them with reporters to protect the children.

The decision to file felony charges against the boys touched off a protest in the Washington area's Hispanic community and attracted national attention, with some parents, lawyers and educators saying that the teacher had overreacted by pursuing criminal charges. Some argued that such charges wouldn't have been filed against non-minority students.

The teacher, Michael D. Searles, was not injured, police said, and school officials had already suspended the boys for the Oct. 12 incident and ordered them to perform community service. The Arlington Education Association has defended the teacher's actions, saying he wanted to make sure that the students got appropriate services.

Hispanic activists expressed relief yesterday that no jail time was imposed, but they said the case still troubles them.

"It should have never gone this far," said Gloria Barajas, of the Arlington Hispanic Parents Association. "Certain children don't get a fair shake. Their parents show up at school with their lawyers and it's quietly taken care of before anything happens . . . when our kids get charged with a felony for basically an inane action."

John Whitehead, president of the Rutherford Institute, which helped one of the boys find a lawyer, said he was pleased that the child did not end up with a felony record.

"That's what we want for our client, as well," Whitehead said of the second boy. "It still doesn't justify the way this was pursued. . . . It's the kind of stuff that I did as a kid, but I had to stay after school for an hour."

Although changes in state law have opened many juvenile hearings to the public, cases involving children so young, and convicted of misdemeanors, remain confidential. Rosa Hernandez, the mother of the boy who will be sentenced Feb. 29, went public in November out of concern for her son. The Washington Post generally does not identify juvenile defendants. Hernandez has a different surname from her son.