AS politicians at all levels of government look to cut spending, taxpayers need to make sure that public employees don’t get a free pass — particularly when it comes to pensions.

Most of the nation’s 107 million private-sector workers are forced to accept 401(k) plans and other

defined-contribution pensions — in which the employer makes a fixed contribution to the employee’s retirement account, rather than guaranteeing a fixed payout.

By contrast, nearly all of the more than 22 million federal, state and local public employees enjoy defined-benefit pensions — with payouts fixed at some percentage of the individual’s pay for the last year or two they worked (often including overtime and payments for unused sick or vacation days).

But funding of public pensions has been woefully short of what’s needed to make good on those promises. The shortfalls are “off balance sheet” liabilities that run into the trillions of dollars.

Here’s the bad news as reported by Professors Robert Novy-Marx (University of Rochester) and Joshua Rauh (Northwestern’s Kellogg School of Management):

* Unfunded liabilities for public pensions run by the 50 states total $3.23 trillion — $21,500 per household.

* Underfunded pensions for municipal and local government employees add another $574 billion of hidden debt — $14,000 per household.

The data from federal sources is also grim:

* Unfunded US military-retirement obligations now amount to $30,000 per household.

* Unfunded federal civilian-employee pension obligations represent another $16,000 per household.

That means every US household (including the half that normally pay no taxes) would have to kick in $81,500 today to enable federal, state and local governments to meet just their cur rent pension commitments.

For residents of some big cities, the news is much worse. For example, New York City’s unfunded pension liabilities alone are nearly $39,000 per household, second only to Chicago at $42,000 per household.

And while many of the 107 million private workers have seen their 401(k)s decimated by investment losses, public employees haven’t had a hair on their heads touched. Because their pensions are fixed, when public-pension investments go south — they underperformed by 30 percent in the first two years of the recession — the taxpayers have to make up the difference.

The inescapable reality: Many cities and counties are unable to pay their pension obligations and will look to their states for bailouts, and many states are broke and will look to the feds — that is, the taxpayers.

Now, the taxpayers are already going to be making sacrifices, because there’s just no way to balance the budget without reducing Social Security and Medicare benefits. Are we going to make those cutbacks even more harsh in order to preserve the lavish fixed pensions enjoyed by public employees?

It’s hard to believe: Private-sector workers will struggle through their old age with small 401(k) plans and reduced Social Security and Medicare benefits, while public-sector retirees live high on the hog thanks to their fixed pensions. (For example, more than 3,700 retired New York state workers now collect more than $100,000 a year for life.)

It’s time to get realistic about living within our means, so Social Security and Medicare (and Medicaid) must be “on the table.” But why should public workers get a free pass at the cost of the rest of us?

We’ve got to bring public pensions into line with the vast majority of private pensions. Apart from military pensions, they should all be defined-contribution plans. That way, governments must pay as they go — so there won’t be unfunded pension liabilities the rest of us have to pay for.

Yes, many current public workers have vested legal rights to their fixed pensions — but the feds can and should tie any bailouts of state and local governments to the public unions agreeing to reduced benefits and conversion to defined-contribution plans for younger and new workers.

That way, public employees can choose between not getting paid an over-the-top pension and getting paid a more reasonable one.