Kenneth William Clark, who has spent much of the last 10 years in Maryland mental institutions after he admitted killing his mother, brother and two sisters in their Rockville home, was captured by the FBI in California this week after his latest escape.

Clark, 26, escaped from the Springfield State Hospital in Sykesville, Md., last February. He had been transfered there from the state's maximum security mental institution and was working through the courts to obtain his release.

Clark was found innocent by reason of insanity in 1969 for the four stabbing and bludgeon slayings. Two psychiatrists had testified that he was a "chronic schizophrenic" who had been deeply troubled all his life.

Clark, then 15, had told police after his arrest that a recurring nightmare in which his 8-year-old brother threatened him triggered his rampage in the family's Rockville home.

After his trial, Clark was committed to the maximum-security Clifton T. Perkins State Hospital. In 1973, he was placed on conditional release. While living in a halfway house, he married, but later attempted suicide and was returned to the hospital.

In May 1975 he eluded a hospital guard who had taken him to the University of Maryland Catonsville campus to seek enrollment, pending another conditional release.

That November, he was arrested by police in Hopkinsville, Ky., and returned to Perkins.

Last year, psychiatrists at Perkins reported to the Montgomery County Circuit Court, which must authorize Clark's release, that Clark was improving. They recommended that he be moved to "a more open setting" at the Springfield Hospital Center. Clark was sent there last fall. He disappeared in February.

FBI agents apprehended Clark in Van Nuys, Calif., last Tuesday on a federal complaint charging him with unlawful flight to avoid confinement, according to the FBI in Baltimore.

He is being held in the Los Angeles City Jail, awaiting an extradition hearing to determine whether he will be returned to Maryland.