Forty-six thousand General Motors workers will continue to stay off the job as they digest a proposal to raise wages and cap health costs — while also closing four plants.

The United Auto Workers agreed to extend the 32-day walkout Thursday amid rumbling from members about a plan that allows GM to not revive auto manufacturing plants in Baltimore, Lordstown, Ohio, and Warren, Mich., that had been closed earlier this year — a major concession by the UAW.

A parts distribution plant in Fontana, Calif. — which had not been previously designated for shuttering — will also shutter, according to the agreement.

The tentative deal was supposed to put a quick end to the costly strike, which has cost GM an estimated $2 billion as production stalls. But the concessions have raised concerns among workers about a lack of job protections and could endanger its ratification, sources said.

As these details came to light Thursday, the optimism that met news of the agreement on Wednesday quickly faded. GM’s hourly workers may still ratify the plan, but the process could take weeks.

“Today it’s us. Tomorrow it could be somebody else,” Tim O’Hara, president of the UAW Local 1112 in Lordstown, told local newspaper Mahoning Matters.

The fight over the Lordstown plant was especially fierce, as President Trump took to Twitter in March to demand GM boss Mary Barra reopen the facility.

“She blamed the UAW Union — I don’t care, I just want it open!” he wrote.

On Wednesday, The Post reported that discussions between GM and the union to bring manufacturing jobs to Lordstown would not likely die with the proposal, even if it were to be approved by members.

On Thursday, a GM spokesman said GM plans to start producing electric-vehicle batteries in the Mahoning Valley in eastern Ohio, which they project will bring 1,000 jobs to the area. Meanwhile, the GM plant in Lordstown will be sold to an e-vehicle company, Lordstown Motors Corp., which plans to create 400 jobs when it opens, the GM spokesman said.

A representative for Lordstown Motors couldn’t be reached for comment.

As part of the concessions extracted by the UAW, full-time workers will get a one-time bonus of $11,000, while temporary employees will get a bonus of $4,500 — but only once the agreement is ratified.

By 2023, all permanent manufacturing employees will make $32.32 an hour., no matter how many years they’ve worked at GM. Workers currently make $17 to $29.24 an hour, depending on seniority.

The agreement will also guarantee wage increases of 3 percent during workers’ second and fourth years. The employees will get a lump sum payout that would amount to a 4 percent raise on their first and third years.

Temporary staffers who work for three consecutive years will be “considered” for full-time jobs starting in January 2020 — an agreement that was first reported by The Post.

The temp workers will also get five days of paid time off, up from three, and will make as much as $24 an hour, up from $17.53.