MILWAUKEE, JAN. 30 -- For almost three hours in a stunned courtroom today, two lawyers described the nightmarish life of Jeffrey L. Dahmer and asked a jury to believe that the confessed serial killer was either an uncontrollable victim of mental illness or a coldly calculating monster who sought to prolong sexual pleasure with the bodies of the men and boys he killed.

With his father, stepmother and relatives of many of his 15 victims sitting nearby, Dahmer listened impassively as his attorney described in agonizing detail how the quiet former chocolate-factory worker fantasized as a youth about homosexual sex with a corpse and eventually descended into a ghoulish world of necrophilia, dismemberment and cannibalism.

"He ate body parts, the purpose of which {was} so that these poor people he killed became alive again in him," attorney Gerald P. Boyle told the jury.

Boyle said Dahmer masturbated before skulls of some victims and performed sex acts on bodies.

But Milwaukee County District Attorney E. Michael McCann said that, despite the horrifying nature of Dahmer's acts, he was always in control of himself, choosing his victims carefully and bypassing other opportunities to murder and dismember because he thought that he might be caught.

Dahmer had sex with those he lured to his apartment here and then killed them to keep control of them, McCann said. He retained their bodies "to extend his time of pleasure" with them, he said.

"His first choice is a totally compliant, living human being," McCann said. "His first choice is not a dead body . . . . He enjoys the bodies for a day or two. Then he tires of it. He doesn't find them sexually attractive. It becomes a disposal problem."

Some of the most grisly details of Dahmer's murderous rampage were recounted later by two Milwaukee homicide detectives who spent hours interviewing him.

In flat, emotionless testimony, Detectives Patrick Kennedy and Dennis Murphy said Dahmer told them that he skinned some victims, cleaned and spray-painted their skulls, preserved body parts in formaldehyde so he could "look at them and masturbate" and kept preserved human hearts in his freezer.

Preparing to eat the bicep of one victim, Murphy said, Dahmer "put Crisco on the bicep, softened it with meat tenderizer and fried it on a skillet."

The lawyers' dramatic opening statements marked the judgment phase in the worst multiple murder case in this city's history.

It began last July 22 when police entered Dahmer's dingy second-floor apartment just west of downtown Milwaukee and found severed heads and other body parts of 11 of his victims. The Dahmer case has horrified, fascinated and deeply embarrassed this city that prides itself as a citadel of midwestern probity and working-class values.

Dahmer, 31, has pleaded guilty to 15 counts of murder but not guilty by reason of mental disease or defect to the same charges. He faces mandatory life sentences on each count unless found not guilty by reason of insanity. Then he would be committed to a state mental institution, also probably for life. Wisconsin does not have capital punishment.

Today's opening statements made clear that the key issue for jurors will be whether Dahmer could control murderous impulses. According to McCann, Dahmer has said he knew his actions were wrong, leaving a claim that he could not control himself as the only basis for an insanity defense.

Boyle told jurors that Dahmer was "not an evil man, this was a sick man," afflicted with the psychological disorder of necrophilia, a desire to have sex with the dead. Recounting Dahmer's life, he described how, as a youth in Ohio, Dahmer was fascinated by the bodies of animals he found on the highway and brought them home to cut up. At 14, Boyle said, Dahmer realized that he was homosexual and first fantasized about having sex with a corpse.

Living with his grandmother in a Milwaukee suburb in the mid-1980s, Dahmer gradually began to lose control of his desires, Boyle said. He stole a male mannequin from a downtown department store, but that "didn't work," Boyle said. He tried to exhume a corpse from a cemetery but failed because the ground was frozen. He visited gay bathhouses, drugging men he met and having sex with them when they were unconscious, until he was caught, Boyle said.

Dahmer is being tried for 15 of 17 homicides to which he has confessed. The first occurred in 1978 in Ohio, where he faces a separate murder count. The body of his second victim, Steven Tuomi, 28, was never found, and Dahmer has not been charged in that case. But Boyle said today that Dahmer's slaying and dismemberment of Tuomi was a critical moment in his transformation into a serial killer.

Dahmer took Tuomi to a seedy hotel, had sex with him and passed out drunk, Boyle said. "When Mr. Dahmer wakes up, he's on top of Mr. Tuomi," Boyle said. "Mr. Tuomi is dead. He knows he killed him, but he doesn't know how . . . . The doctors will tell you that, when he wakes up in the Ambassador Hotel, it was over. Mr. Dahmer would continue to do this until it was stopped."

Boyle also confirmed a published report that Dahmer tried to perform crude lobotomies on some victims. "He wanted to create zombies, people who would be there for him," Boyle said.

Boyle also said Dahmer became obsessed with two movie characters -- the emperor in "Return of the Jedi" and Satan in "The Exorcist III." Dahmer bought yellow contact lenses in an attempt to resemble the emperor and felt that "because of what he was . . . there was no other entity to relate to other than Satan," Boyle said.

McCann said he will present evidence of Dahmer's close control of his actions, including the fact that Dahmer carefully chose victims who did not have cars because he knew automobiles could be used to trace missing persons.

"This is about a man who had sexual desires for men but didn't want it to end there," McCann said. "He wanted it to continue on his terms. That is what this is about."

McCann also said Dahmer has told a psychiatrist that he would not have killed any of his victims if they had agreed to stay with him for two or three weeks. "He wanted the pleasure of them alive," McCann said.