LOS ANGELES, May 31 — Leslie Van Houten said at her third murder trial she was so heavily drugged on LSD that she was incapable of functioning on her own and mindlessly carried out Charles Manson’s orders to kill.

Miss Van Houten, now 28, began testifying in her own defense Tuesday at her murder trial for the slayings of grocery chain owner Leno LaBianca and his wife, Rosemary, in 1969.

“I was more comfortable on LSD than I was off,” she said.

Responding to questioning by defense attorney Maxwell Keith, Miss Van Houten repeated testimony she gave at her second trial about the effects of drugs.

“I found security in LSD. The more I took it the more I couldn’t relate daily to regular kinds of people … the stranger they looked to me.”

Miss Van Houten said she also used mescaline, hashish, opium, TCP, menthradine, benzadnne, psilocybin and marijuana.

Miss Van Houten was found guilty of first degree murder in 1970 and sentenced to death along with Manson, Susan Atkins and Patricia Krenwinkel, who also were convicted of killing actress Sharon Tate and four others the night before the LaBianca slayings.

Her sentence was reduced to life under a State Supreme Court ruling against capital punishment and she was granted a new trial on grounds her case should have been severed from the others when her attorney vanished during the first trial.

She was tried again last year but the jury was unable to reach a verdict and a mistrial was declared.

Her third trial has been under way for three months. She is free on $200,000 bail after spending more than eight years behind bars.