The Democrats’ multi-trillion-dollar social-infrastructure spending plan includes a “Schumark” — a $40 billion earmark championed by Senate Majority Leader Chuck Schumer for the New York City Housing Authority. This manna from Washington is just the sort of half-baked borrow-and-spend scheme that has Sen. Joe Manchin threatening to torpedo the bill.

There’s no doubt America’s largest public-housing system — with 178,000 apartments in 324 developments, it accounts for 13 percent of all such units nationwide — needs to address its litany of maintenance woes: leaky roofs, rampant mold, broken elevators, a lack of security systems and, notoriously, lead paint.

But a huge federal-fund infusion won’t save NYCHA: It needs fundamental change in how it operates, not what amounts to a blank check. Handing it a pile of cash would undermine the first creative management approaches the authority has undertaken since its inception. The Dems assume that NYCHA’s only problem is a lack of funding — and that’s not so.

The stakes here are high. This city-in-a-city is home to as many as 600,000 residents; the Community Service Society declared in a 2014 report that “NYCHA reached a point where it might have qualified as the city’s largest and worst landlord.”

But NYCHA didn’t get that way because of “federal disinvestment,” as Democrats and their allies charge. There’s no reason to be confident that, absent changes, it will spend that borrowed money well.

Authority management, unlike Gotham’s many well-run property-management firms, is hamstrung by no fewer than 30 labor unions, whose contracts can limit work to weekdays, 8 a.m. to 4:30 p.m. The inevitable emergency repairs require overtime — or simply fester.

The federal monitor appointed to oversee the authority’s operations put it this way: NYCHA is “fraught with serious problems in structure, culture, and direction, and perhaps even worse.” Just this week, The City reported that NYCHA workers “covered up signs of mold” at five different developments, “falsely claiming that there wasn’t enough moisture to require a cleanup.” NYCHA has charged seven workers with lying to avoid performing mold abatements.

A federal bailout — no questions asked — would not fix any of this. Worse, it would short-circuit the imaginative ideas NYCHA CEO Greg Russ has advanced to tap into private funding and create a management authority with wider latitude. His “blueprint” would put 110,000 units in a Public Housing Preservation Trust that would allow it to tap private funding. The Legislature, which has to approve the plan, refused even to take it up in the last session. An additional 62,000 units would move into direct private management.

There’s simply no reason to spend public dollars when private investors can be drawn to repair and better manage the aging apartments. Think of the Schumark as union protection.

NYCHA needs inventiveness. As matters stand, more than a quarter of the residents are “overhoused” — in apartments with empty bedrooms. The average stay is almost 20 years, and 10 percent of residents have lived in public housing for more than 40 years.

Many of the buildings sit on valuable real estate that could be sold to pay for renovating a smaller system. Rather than displacing tenants, the sales proceeds could buy them out — and free them from a crippling dependence.

Public housing has been a disaster for black Americans, who make up 45 percent of NYCHA tenants and 47 percent of public-housing users nationwide. Neighborhoods in which there was extensive minority-owned property were razed — and replaced by the projects, in which no one but the government can own anything and no businesses even operate. It’s no wonder the gap between black and white home-ownership was smaller in 1934 than it is today.

The essential public-housing model has to be rethought. To the extent it’s retained, it must become transitional housing — with a five-year ceiling — that enables tenants to save money and then move up and out.

The Schumark will leave in place a dysfunctional system that only benefits labor-union members and robs residents of the chance to own and accumulate wealth. Such is the collateral damage of what is true housing socialism: government ownership and operation. It’s time to stop subsidizing it and humanely phase it out.

Howard Husock is a senior fellow at the American Enterprise Instituteand author of the new book “The Poor Side of Town.”