In the first fatal shooting this year by Prince George's County police, a sergeant yesterday killed a man who threatened his mother with a knife in the bathroom of their Landover Hills apartment, authorities said.

Police sources said Eric Stewart, 31, was shot once in the head after he disobeyed orders to drop the knife and swore that he would kill his mother. The shot was fired, police sources said, by Sgt. Russell Watson, a 28-year officer who in March was instrumental in persuading a homicide suspect not to jump from the Woodrow Wilson Bridge.

The sources said patrol officers had become familiar with Stewart's erratic behavior in recent months. On Nov. 9, police responded to a report of a domestic dispute at the two-bedroom apartment in the 4100 block of Warner Avenue. According to police records, Stewart was behaving oddly that night and saying that his sister wanted to kill him. The officers were able to quiet the situation and left.

The 1,400-member department led the nation in fatal shootings per officer during the 1990s, but the rate has dropped dramatically in recent months. Last year, police officers shot seven people, two of them fatally. Yesterday's shooting was the second by an officer this year and the first that resulted in death.

Police Chief Gerald M. Wilson said the reduction was a result of 18 months of department-wide retraining and the introduction of less lethal weapons to the department's arsenal.

"Every day, officers are called into a situation where force might be needed," Wilson said. "We have lots of tools in our chest for those situations, and generally they're able to use those various tactics to resolve the situation."

But yesterday, Wilson said, officers from the Conflict Management Team, "based on the precipitous nature of the suspect's actions, felt we had to stop him from potentially taking the life of his mother."

"There was an indication that this person was unstable, but . . . his physical actions were clear, and he just wouldn't cooperate," he said. "It's a tragedy every way you look at it. There's someone dead who didn't have to be and there's an officer who has to live with this forever regardless of the heroic nature of it."

The two-hour drama that ended in Stewart's death began when someone called 911 shortly after midnight to report that Stewart was threatening his mother, police said. When officers arrived, Stewart was holding a knife to his mother's neck, Wilson said. He said the officers called for an ambulance and the police Conflict Management Team, a 70-person unit that includes Watson's squad, negotiators and hostage technicians.

"They tried initially to persuade the individual to surrender," Wilson said. "At some point during the standoff, the suspect's movements were such that the supervisor of the SWAT team who is responsible for security there on the scene felt he was about to lose control of the situation and that death to the mother was imminent, and so he directed a member of his team to shoot."

Police sources said Stewart had dragged his mother into the bathroom, was using her as a shield and was shouting profanities and threats to cut her throat when the order was given to shoot him. They also said the mother was yelling for help.

"If you've got a knife to someone's throat and you're standing behind them and there's no way to get behind the suspect, it makes it impossible to deploy less lethal force," Wilson said. "The action police take has to accomplish the task right then and there. You don't get a second chance."

Police said Stewart's mother, whose name they did not release, was treated for a minor knife wound to her arm. She could not be reached for comment yesterday.

Court records show that Stewart had a history of assault charges and was jailed last summer.

Wilson said the shooting appears justified, but he said an investigation will be conducted and its findings forwarded to the interim state's attorney, Glenn F. Ivey, who will decide whether to present the case to a grand jury. County Executive Jack B. Johnson (D), who during eight years as state's attorney prosecuted several police officers accused of misconduct, could not be reached for comment yesterday.

One of his spokesmen said Johnson was aware of the shooting but had nothing yet to say about it.

Researcher Margaret Smith contributed to this report.