Alexandria police and other area police departments said yesterday they rely on frequent training and common sense, not specific rules, to prevent off-duty accidents involving officers' service revolvers like the apparent accident that killed an Alexandria boy Tuesday.

John Joseph Staus, 12, was fatally wounded when a police revolver issued to his stepfather, an 11-year-veteran of the Alexandria police force, discharged during a game of cops and robbers in the family apartment on Duke Street.

Area police said it would be difficult to devise a specific code on how officers should store and handle their guns at home.

"It would be hard to enforce one if there one was one. The only way you could enforce that is to surprise them at home and that you can't do," said Sgt. William O'Donnell of Fairfax City police.

Officials from area police departments, including Alexandria, said yesterday that they train officers at least once a year on gun safety and the cleaning, handling, and storing of firearms. In addition to training, officers are tested in firearm use and safety in order to be qualified to carry revolvers, officials contacted yesterday said.

They said however that departments often leave revolver storage to the discretion of officers.

Departments also say that the officer should use his own judgment in deciding how to store a revolver at home.

In Alexandria, the police department advises its officers to store their service revolvers "in a high place, in a closet, maybe in a secure place that can be locked," said Cpl. Ralph Carlton.

According to police accounts of Tuesday's incident, Staus was holding a toy gun when his stepfather, William R. Trotti, who was holding a .38 caliber service revolver, turned toward him. At that point the gun, which Trotti thought was unloaded, discharged, police said.

A preliminary police investigation has determined that the shooting was accidental. The police, along with the Alexandria Commonwealth's Attorney's Office, are continuing to investigate the incident.

Area officers are allowed to take their service revolvers home because officers are on duty around the clock, police said. However, Falls Church police encourage officers to leave their guns in their station lockers and most of them do, said Deputy Chief Timothy Toureau.

Police report that accidental discharges of revolvers while an officer is off-duty are rare.

In 1957, the Falls Church chief of police accidentally shot and killed a close friend when his revolver discharged as the chief was demonstrating a police method of searching a prisoner.

In Prince George's, police said there were three accidental discharges in 1981 and six in 1982, Smith said. About five years ago, a Prince George's officer's wife was wounded by an accidental discharge of his revolver. More than two years ago, an officer accidentally wounded his brother with a gun.

Prince George's officers involved in accidental discharges of their guns are normally fined between $50 and $250 for the first offense.