TRACY, Calif., Apr. 16 — Manson family member Robert (Cupid) Beausoleil was stabbed in the heart with a prison-made knife in a wing for honor inmates at Deuel Vocational Institution, prison officials said today.

Beausoleil, 34, convicted in the torture-slaying of a Los Angeles musician, was in critical but stable condition on a respirator at San Joaquin General Hospital in Stockton.

He was stabbed in the chest and back Thursday at 9:30 p.m. with a 10-inch piece of sharpened metal that may have been broken off a fixture, prison spokesman Cliff Reed said. The assailant was unknown.

Beausoleil ran out of his wing into the arms of prison staff members. The unit was occupied by about 240 inmates, who have keys to their own cells and were permitted to move freely at the hour of the attack.

Beausoleil returned from a five-month psychological and neurological examination at the California Men’s Colony in San Luis Obispo on April 8. The study was to determine his readiness for parole.

Beausoleil, who lived with Charles Manson in 1968, was convicted and sentenced to death in April, 1970, for the July 27, 1969, stabbing death of musician Gary Hinman, 34, at the victim’s Topanga Canyon Home.

He had been on Death Row at San Quentin Prison but was transferred to Deuel after a U.S. Supreme Court decision ruled the death penalty unconstitutional.