LOS ANGELES, Calif. — The Board of Supervisors agreed today to consider building a treatment center to house mentally ill inmates as one of several alternatives to a proposed $933 million rebuild of downtown Men’s Central Jail.

Supervisor Zev Yaroslavsky recommended the treatment center be added to options being studied to solve jail overcrowding at the urging of Assistant Sheriff Terri McDonald, who oversees the county jail system.

“Law enforcement agencies have unfortunately become the caretakers of last resort for many of these mentally ill individuals” Yaroslavsky said, echoing Sheriff Lee Baca’s sentiment that the county’s jail system has become the “largest de facto mental hospital in the nation.”

Under the proposal, part of Men’s Central Jail would be demolished and replaced by a new facility designed to address inmates’ mental health, substance abuse and ongoing medical conditions like diabetes and kidney disease. Mentally ill prisoners, including those with substance abuse disorders, would be jailed in the new center rather than as part of the general population.

Other options to expand jail capacity include housing women prisoners at the former federal immigration Mira Loma Detention Facility, renovating Pitchess Detention Center and sending inmates with long-term sentences to a former state prison in Kern County run by the city of Taft. Officials are also looking at alternatives to incarceration such as electronic monitoring, pre-trial release programs and community-based social services.

As many as 60-70 percent of county inmates are drug abusers, according to the Sheriff’s Department.

Yaroslavsky said state correctional officials were already moving in a similar direction, opening a facility in Stockton for prisoners with mental illness or medical conditions.

The plan would free up needed jail beds, the supervisor argued, because some prisoners with special issues are now assigned to solo cells, taking up two beds.

Civil rights activists supported the plan, but told the board it did not go far enough.

Peter Eliasberg, legal director of the American Civil Liberties Union of Southern California, said he hoped the county would consider more than “just a better jail model,” arguing that most mentally ill inmates should not be in jail at all.

Eliasberg wants outside mental health advocates to have a voice in the process and expressed skepticism about the ability of the Sheriff’s Department and Department of Mental Health to come up with a new solution to a decades-old problem.

“Twin Towers (Correctional Facility) was promised to be better treatment of the mentally ill,” Eliasberg said, referring to the downtown jail built in 1997.

Marsha Temple of the Integrated Recovery Network, which works with the homeless, cited “the revolving door between Skid Row and Twin Towers” and advocated for “community-based treatment that would provide housing, health care and jobs and thereby reduce recidivism and keep mentally ill people out of jail.”

Yaroslavsky said he wasn’t sure the treatment center would work, but he asked staffers to evaluate the option and allowed for the possibility that it could be a “game changer.”

More importantly, he said, “I’m not interested in spending a billion dollars on another jail. I just think that’s a colossal waste of money.”

But the county is under federal mandate to reduce overcrowding even as the inmate population increases — in part because of a state move to shift low-level offenders to local jails.

A consulting firm doing a review of jail facilities and projecting the need for beds over the next 30 years is expected to deliver a report to the board by July 16.

The board’s vote in support of Yaroslavsky’s proposal was 4-0.

Supervisor Gloria Molina was absent.