A clinical psychologist retained by defense attorneys for Chander "Bobby" Matta concluded that Matta was suffering from a mental disease when he allegedly killed three Washington-area prostitutes during the Memorial Day weekend.

The psychologist, R. Bronson Levin of Alexandria, wrote in a report filed yesterday in Arlington County Circuit Court that Matta, 22, "had an irresistible impulse to obey command hallucinations" at the time of the killings.

In his report, Levin also concluded that Matta's "highly religious and sexually repressive" upbringing in a home "where the role of women was a source of perpetual parental argument" contributed to those impulses and to Matta's sexual repression.

"Mr. Matta equated his own sexual impulses with sinfulness . . . . Haunting guilt followed sexual acts," Levin wrote. "This otherwise law-abiding man was driven to express these conflicts."

Matta "understood the nature and the wrongfulness of the acts, but was not in willful control over his actions" at the time of the slayings, Levin wrote.

The finding supports the claim by defense attorney William B. Moffitt that Matta was insane at the time the killings occurred.

The prosecution has argued that Matta's behavior was calculated, and not the behavior of a man suffering from a mental defect.

Matta is charged in the slayings of Jody Marie Phillips, 16, Sandra Rene Johnson, 20, and Sherry K. Larman, 26. The women were asphyxiated within a 36-hour period. Matta described in a statement to police how he used a lethal choke hold on each woman after having sex with them.

Levin met with Matta four times after he was arrested and charged in the slayings on June 10. He also has met once with Matta's former girlfriend and is scheduled to meet with Matta once more before his first trial, which will be for the Phillips slaying. The trial is scheduled for Jan. 22.

Levin wrote that the weekend Matta allegedly killed the women was the first time he had been left alone in the family's South Arlington home. Matta's parents and a younger brother were away at a Sikh religious retreat during the holiday weekend.

Levin wrote that among the factors that caused Matta to lose "the internal controls over his thought processes and actions" were his lack of success at college and his girlfriend's rejection.

Matta broke up with his longtime girlfriend and withdrew from college after receiving poor grades shortly before the slayings occurred.

Levin did not return telephone calls yesterday.

Thomas C. Goldman, a Washington psychiatrist specializing in forensic psychology, said yesterday that evidence that a defendant is suffering from command hallucinations is "one of the strongest findings that a psychiatrist can make in an insanity defense."

Those who suffer from auditory hallucinations, Goldman said, literally hear voices shouting, "Do this, or do that," he said.

But, he said, "it's also the easiest thing to fake. Everyone knows that crazy people hear voices and there's no objective way to verify" it.