The portrait of an "angry, depressed adolescent" - fatherless, left alone by a working mother, struggling to make friends but always failing - emerged yesterday as the defense opened it case in the Montgomery County murder trial of 16-year-old Paul Wersick.

Defense Attorney J. James McKenna, in his opening statement to the jury, first painted this picture of a frustrated youth and then conteded that last July 10, Wersick's mind "blew with an explosion in his head" at the moment tax assessor George Angerman Jr. was fatally shot.

Wersick has pleade innocent by reason of insanity to charges that he robbed Angerman and shot him once in the head. Angerman's body was discovered in the driver's seat of his car, which was parked in an underground garage in Rockville. He gagged with a boy scout neckerchief adn his left wrist was tied with a rope.

Wersick was in a "tranitory psychotic state" when Angerman was killed in Rockville underground garage, and the youth had been in a "fit of infantile rage" from the moment he left his Wheaton home July 10, setting out "to make somebnody feel as bad as he did," McKenna told the jury.

Wersick, then 15 years old, had been upset for a month because he had been "grounded" by his mother for misbehavior, McKenna said.

"You might say 'So what, he was grounded, did he have to go out and do something horrible to someone?'" McKenna told the 12 jurors. "What I'm suggesting is you have to judge this young man individually . . . look at him, his world."

This world consisted of a constant struggle to "relate to other people," particularly at school, McKenna told the jurors. "You'll hear he did funny things, like making up his face . . . but the harder he tried, the more it seemed his effort were in vain."

Wersick "has been reaching out all his life," the attorney said, turning to the short, pudgy youth at the defense table. "He doesn't want to be a bad guy."

Called as the defense's first witness, clinical psychologist Rona Eisner testified that Wersick is a "borderline personality," capable of "falling apart, becoming disorganized at time of stress and pressure."

The youth was having a "psychotic episode" and was in "a state dominated by rage" when he left his house with a gun last July 10, she testified.

Eisner testified that during the crime Wersick's mental state met Maryland's legal definition of insanity-lacking "substantially capacity to appreciate the criminality of his conduct or conform his conduct to the requirement of the laws."

But under cross-examination by Assistant State's Attorney Michale Mason, Eisner was asked why Wersick, in his rage, had not killed other people whom he saw last July 10, but instead had waited to kill Angerman in a secluded garage.

"One reason might be that he was afraid of getting caught," Eisner answered.

"Why would the defendant have cared . . . if he didn't know what he was doing was wrong?" Mason asked.

Eisner answered that "a tiny infant fears getting caught, but does not know right from wrong."