Two 12-year-old District of Columbia boys were found guilty in federal district court here today of the second-degree murder of a 7-year-old boy who was killed last Easter when the older boys tried to take his bike, defense lawyers announced.

The boys were charged and tried as juveniles in the death of Carl Ellis Arthur, of Livingston Road SE, who drowned after being pushed into the Potomac River near Oxon Hill Children's Farm. Police alleged that older boys hit him with a baseball bat and then threw rocks at him until Carl backed into deeper water and drowned.

After hearing testimony in a two-day trial, which was closed to the public, Judge John R. Hargrove Sr. found the two boys, one from Northeast Washington and the other from Southeast, guilty of robbery, attempted robbery, assault with a deadly weapon and second-degree murder.

The boys, whose names are not used because they are juveniles, will be sentenced Aug. 8. The maximum sentence is detention in a juvenile facility until age 21.

After the trial, defense attorneys Linda Spevack and Elvira White said that their clients indicated that they did not fully understand the implications of their trial and expressed concern about what would happen next. "I explained to him, but he still gave me a blank stare," said Spevack about her client's reaction to the verdict.

Spevack said that her client had sat through the two-day proceedings "with his fingers in his mouth."

"What is so ironic and sad about the entire thing . . . is my client doesn't understand or know the impact on his total life," White said as she stood outside of the courthouse.

The mothers of the two boys would not comment after the trial.

U.S. Park Police reported earlier that they believed Carl had met the boys near a playground of the federally owned Oxon Run Park and that they had gone bike riding along a path to Oxon Cove, where the older boys decided to steal his bike.

A District harbor police unit found the first-grader's body in Oxon Cove shortly after 9 p.m. on Easter after one of the boys told his father about the incident, prompting the father to call police.

Defense attorneys said that testimony never revealed whether Carl knew the two older boys. U.S. Park Police had said at the time of the investigation that they did not believe Carl knew them.

The boys' cases were switched from a Maryland state court to the federal court after officials determined that the state did not have jurisdiction over the Children's Farm, which is on federal property. The move had caused some concern among White and Spevack, who said again today that they fear the federal government does not have appropriate facilities and programs for juveniles.

Both attorneys said that the mothers of their clients had expressed a desire to see their children kept close to home. Both youths are being detained at a state-run facility in Northern Virginia and will remain there until the Aug. 8 sentencing, the lawyers said.

After the trial, Spevack and White said they did not know how much of a part the children's environment had played in what had happened. "How does one gauge society so these things don't happen?" Spevack asked.