In a court hearing that gave a detailed look into the bizarre world of a troubled man, Mark David Chapman, who earlier this summer pleaded guilty to the murder of John Lennon, was sentenced to 20-years-to-life in prison today.

There was no response to the sentence from the 26-year-old Chapman, who has said repeatedly that Satan told him to kill the rock star.

Pale and wearing a bulky bulletproof vest that was clearly outlined beneath a short-sleeved prison shirt, Chapman sat impassively. He clutched a worn, red paperback copy of "The Catcher in the Rye," a book he had in his possession the night of the shooting last December, a book which he feels tells his story.

But when asked if he had anything to say, he rose quickly and calmly, and said politely that he wished to read a brief passage from "The Catcher in the Rye," a passage, he said, that would be his "final spoken words." The passage that followed seemed to be an attempt at moral justification, Chapman's vision of himself -- though he had shot Lennon four times at point blank range -- as protector of the weak and innocent.

"Anyway, I keep picturing all these little kids playing some game in this big field of rye and all," he read. "Thousand of little kids, and nobody's around -- nobody big, I mean -- except me. And I'm standing on the edge of some crazy cliff. What I have to do, I have to catch everybody if they start to go over the cliff -- I mean if they're running and they don't look where they're going . . . . That's all I'd do all day."

A former security guard in Hawaii with a history of mental illness, Chapman had pleaded guilty to killing Lennon outside the fashionable New York apartment building where the 40-year-old former Beatle lived. That plea, in State Supreme Court this June, was made over the objections of court-appointed attorney Jonathan Marks, who had counseled Chapman to plead innocent by reason of insanity. His advice was ignored. God, Chapman told Justice Dennis Edwards Jr. in a closed hearing, told him to plead guilty.

This morning, in state Supreme Court, Marks once again tried to have that guilty plea dismissed and requested new psychiatric tests for Chapman.

Edwards refused that request, saying, in sentencing, that Chapman was aware of his actions.

"The defendant has stated, 'I intend to kill John Lennon' , " the jurist said. " . . . When asked why he used hollow bullets, he said, 'to ensure John Lennon's death ' . . . There is no doubt in the court's mind that he is accountable, responsible."

Assistant District Attorney Allen Sullivan, in his summary comments, also insisted that Chapman had been aware of his actions -- that he had, in fact, decided to kill Lennon in a "deliberate, cold, calculated plan . . . in order to draw attention to himself, to gain fame."

"In a sense it was a media crime, he planned his crime so he would gain public attention," said Sullivan, as he called on the court for a maximum sentence. "What he wanted is what he got . . . . He's received attention beyond his wildest imagination . . . . He wanted to be famous, to be noticed . . . The person he tried to convince to remain outside Lennon's apartment house on the night of the murder was not a person who had been friendly to him, it was a photographer . . . someone who had been unfriendly to him . . . but he wanted to be as famous as possible."

Defense attorney Marks disagreed. While stating that Chapman was "not a sane man" and was, moreover, "a very dangerous man," he asked that the court show mercy and that Chapman receive psychiatric treatment.

"The irony of this case is that I don't believe that Chapman understands why he is here . . . I don't believe that he understands the charges against him," said Marks.

Prior to the sentencing, the court was given vivid testimony of Chapman's condition by two defense psychiatrists. Both agreed that Chapman was psychotic, and one, Dr. Daniel Schwartz, a forensic psychiatrist who had examined Chapman half a dozen times, diagnosed Chapman as a paranoid schizophrenic and narcissistic personality who was also delusional and suffered hallucinations. He painted a detailed picture of Chapman's world, a world filled with gods and demons; a world in which Chapman ruled over an imaginary kingdom of little people.

Chapman, according to Schwartz, had lived in this imaginary world since the age of 9 or 10.

"He had difficulty with socializing or relaxing with his peers," said Schwartz. "He was very much a loner . . . and so he invented a world of imaginary little people, in which he imagined himself a grandiose ruler . . . . He told me, 'I had control of their lives, they worshiped me like a king' . . . He also likened his position to that of men and God."

Chapman's imaginary world, said the psychiatrist, was "very real" to him, a way of "discharging any aggressive feelings he had . . . he never learned to deal with his feelings of anger or aggression, I'm afraid."

Chapman could "wreak havoc" on his kingdom when displeased, or, "as a benevolent king," reward his people with rock concerts. By the time he reached high school, his fantasy world changed. At that time, though the little people still existed, Chapman felt his brain had become three computers. Later, those computers were replaced with yet another world, filled with an imaginary government.

The psychiatrist testified that Chapman's moods could change very quickly and that he had had "several major depressive episodes."

"He told me he didn't just believe in Satan, he knew Satan," said the psychiatrist.