The New Orleans City Council took a unanimous stand Thursday against Sheriff Marlin Gusman’s plan to build a multimillion-dollar jail for special needs inmates, rejecting the idea as a wasteful investment for a community seeking to scale back its notoriously high incarceration rate.

The council, in a 6-0 vote, urged the sheriff in the same resolution to stop housing hundreds of state prisoners and Plaquemines Parish inmates at Orleans Parish Prison — a nonbinding demand intended to reduce the city’s jail population and increase the ratio of deputies to inmates.

Instead of constructing a new lockup, a building that supposedly would cost between $56 million and $97 million and contain between 380 and 764 beds, council members want Gusman to agree to retrofit the fourth floor of a 1,438-bed jail that is under construction by adding medical and mental-health care units — a move that would reduce the jail’s total capacity by some 88 beds and cost about $6 million.

A Gusman spokesman issued a pointed response to the vote, dismissing the resolution as lacking in “substance and detail.” The spokesman, Philip Stelly, also accused city officials of shirking their duty under state law to provide a sufficient jail.

“Habitually saying ‘no’ is not a sustainable policy position and is a serious threat to public safety,” Stelly said in a statement.

The council’s vote marked the latest salvo in a bitter feud between Gusman and Mayor Mitch Landrieu’s administration over how to implement a plan for jail reform approved by a federal judge.

Gusman so far has failed to carry out the majority of the changes spelled out in the federal consent decree, which took effect last year after inmates filed suit over the jail’s deplorable conditions. Several of the decree’s provisions require improved treatment of mentally ill inmates.

Such inmates require more careful supervision, suicide-resistant cells and housing that’s separate from the general jail population.

U.S. District Judge Lance Africk has said that OPP’s mentally ill inmates must be transferred out of the facility now housing them, an aging structure known as Templeman V, and last week he ordered the city to pay for housing them temporarily at a state prison in St. Gabriel.

Gusman long has envisioned the construction of a so-called Phase III jail building that would accommodate mentally ill inmates as well as other special populations, saying that it could be paid for with hurricane recovery dollars from the Federal Emergency Management Agency.

The City Council, however, gave its clearest indication to date Thursday that it opposes construction of another new jail, a stance that raised the question of whether Africk ultimately will have to decide himself whether the city needs such a facility to satisfy the terms of the consent decree.

“The ultimate size of the new jail will have substantial and long-term fiscal and public-safety impacts on our entire city,” Councilwoman Susan Guidry said. “I believe it’s absolutely critical that we get this right.”

Because an earlier city ordinance requires Gusman eventually to close OPP’s dilapidated buildings after the new 1,438-bed jail opens next year, the sheriff has said a Phase III building will be necessary if for no other reason than the size of the city’s inmate population, which as of Wednesday morning stood at 2,116. Nearly 500 of those inmates are Department of Corrections prisoners serving state time.

City officials have objected to that arrangement at a time of dangerously low staffing levels in the jail, saying it also makes no sense financially because it costs more to house DOC prisoners than the state pays the Sheriff’s Office.

The resolution passed Thursday calling for state prisoners to be removed included an exception for state inmates participating in work-release, community service or re-entry programs. However, Guidry warned, “We do not mean for more people to be put into that category so that more DOC inmates can be kept here, and we’ll be looking at that very carefully.”

In an interview earlier this month, Gusman said OPP’s state prisoner population is not nearly as dispensable as some city officials believe, noting that 40 state prisoners were working in the jail’s kitchen as of early June. About 150, he said, had some kind of open charge in Orleans Parish in addition to their state conviction, requiring they remain within close proximity to the courthouse and their defense attorneys.

As of Wednesday, the Sheriff’s Office also was housing 73 Plaquemines Parish prisoners at its Temporary Detention Center while that parish’s new jail remains under construction. Gusman has refused to relocate those inmates, saying the temporary center was intended to include that population when FEMA agreed to pay for its construction.

Follow Jim Mustian on Twitter, @JimMustian.