MILWAUKEE (AP) _ The judge in the Jeffrey Dahmer insanity trial called a witness of his own today after the defense rested its case, a court-appointed psychiatrist who said Dahmer is ''very sick'' but not legally insane.

''Jeffrey Dahmer could best be described as an organized, non-social, lust murderer,'' Dr. George Palermo said after he was called to the stand by Milwaukee County Circuit Judge Laurence C. Gram Jr. ''He's not such a bad person, even though he did what he did.''

The judge questioned Palermo after telling jurors he had the prerogative of hiring a neutral expert who represented neither the defense nor the prosecution.

Dahmer is a ''very sick person'' but ''is not legally insane,'' Palermo said. ''Wherever he goes, I think he should receive treatment.''

Palermo said he didn't believe that Dahmer drilled holes into some of his victims' heads while they were alive, which Dahmer said he did to create zombie-like sex partners who would stay with him.

Palermo said that, based on his interviews with the medical examiner and the holes in the skulls, he believes the drilling ''probably was done ... after the victims' deaths.''

He said he believes Dahmer might have embellished his accounts of the murders when he talked to police, telling them what he had fantasized about doing to the victims instead of what had actually done.

Palermo, who said he interviewed Dahmer four times, will be followed by prosecution witnesses.

Earlier, the judge denied a prosecution request to bypass the jury and immediately declare Dahmer sane. If Dahmer is judged sane at the time of the killings, he could be sentenced to life in prison. If insane, he could be hospitalized and eventually could petition for release.

Dahmer, 31, has pleaded guilty but insane to murdering 15 young men. His lawyers must prove that he could not tell right from wrong or that he was unable to prevent himself from committing the crimes.

The defense has argued that Dahmer's necrophilia, or compulsion to have sex with corpses, is a mental disease and he was uncontrollably driven to kill to satisfy his urges.

District Attorney E. Michael McCann argues that necrophilia is not a mental illness under state law, but rather a personality disorder.

On Wednesday, a psychologist who says Dahmer had a compulsion to kill and have sex with the corpses acknowledged Dahmer let three men go - one of them because Dahmer had to get to work and didn't have time to kill him.

Testifying for the defense, University of Arizona psychologist Judith Becker said Dahmer ''has a mental disease and that's what drives his crime.''

But under cross-examination, she said Dahmer didn't kill one boy he had struggled with, and spared a man to whom he ''was not as attracted ... as he thought he would be.'' He also freed a young man because he had to go to work, she said.

Dr. Carl Wahlstrom, a Chicago psychiatrist, was the last witness for the defense, which began its case a week ago. He said Dahmer was aroused by what he found when he slashed his victims' stomachs.

''He was surprised to see so many colors in the internal organs - red, blue, yellow. He got sexually excited,'' Wahlstrom said.

Wahlstrom said in the weeks before Dahmer's July 22 arrest, he killed at such a rapid rate - four men between May 27 and July 19 - that he became disorganized and ''the bodies were piling up.''

But during Wahlstrom's cross-examination, McCann said Dahmer was ''cunning'' and his stories were ''a manipulative bunch of lies.''

Dahmer has admitted killing 17 young men since 1978 - 16 in Wisconsin and one in Ohio. Prosecutors said there is insufficient evidence to charge him with one of the Wisconsin slayings. He will stand trial in Ohio later.