Four Arlington youths have been arrested in a firebombing incident that caused minor damage to the home of Virginia state Del. Warren G. Stambaugh last week, according to Arlington authorities.

The four, who range in age from 13 to 15, face charges of arson and the manufacture, possession and use of a firebomb in connection with an incident that authorities say apparently arose out of a grudge against the legislator's teenaged son. The charges are felonies.

"For lack of a better word, I would have to describe the motive as a prank," said Arlington Deputy Fire Marshal Mark L. Penn.

"They weren't trying to burn the house down. They didn't know what fire could do," Penn said.

According to investigators, Stambaugh's front porch was hit by a firebomb last Wednesday evening while the family was at a movie.

The bomb, a beer bottle filled with gasoline, missed a window by less than an inch and bounced onto the porch and down the steps, the investigator said.

The flames damaged the porch, a door frame and a bush before they were doused by a neighbor.

"It could have burned the house down," said Penn. "The Christmas tree was right inside that window."

A preliminary hearing was set for Jan. 18 in Arlington juvenile court.