New MTA reporting shows farebeating on buses and subways is still rising — a clear warning that broader public disorder is ahead.

Just what New York needs when Mayor Adams is looking to shrink the NYPD.

Reminder: A crackdown on farebeating was the first major step in the city’s historic gains against crime starting back in the 1990s.

Bill Bratton, then chief of the MTA police, directed that effort in order to make the subways safer: If you commit a casual crime to enter the system, he realized, you become more likely to commit worse crimes while you’re there.

Or to have already committed them: Running the rap sheets of arrested farebeaters turned out to ID lots of perps that police already wanted on more serious charges.

Oh, and the farebeating arrests also caught a lot of illegal-gun-toters.

This was the first practical demonstration of “broken windows” policing, an approach built on the realization that small crimes, left unpunished, lead to larger ones — both by creating the perception that an area is lawless, and by removing consequences for someone’s (usually a young someone’s) first step toward routine anti-social behavior.

After taking over the NYPD, Bratton used “broken windows” (along with reforms that held cops, especially commanders, responsible for actually bringing down crime) to launch New York City’s historic, two-decade success against crime.

But once Gotham became the nation’s safest major city, progressives began to undermine broken-windows policing.

And one key turning point was then-Manhattan District Attorney Cy Vance’s 2017 decision to stop prosecuting farebeating cases (a policy other DAs then copied and Vance successor Alvin Bragg continues), arguing that it wasn’t worth the trouble.

Naturally, farebeating began to creep up, then soared during the pandemic.

And far worse crimes, from murder on down, soared as well — encouraged also by other progressive victories like the Raise the Age and no-bail laws.

Now the MTA estimates that farebeating cost it a stunning $690 million last year — up from $225 million in 2018 — and likely to be much higher this year.

That’s a canary in a coal mine: Place your bets on overall crime heading back up, too, erasing the modest gains Adams has been able to foster.

A recent example of how the disorder metasticizes is the mugging thwarted by a gun-toting straphanger, which began with a perp offering free entry, then demanding compensation.

MTA chief Janno Lieber gets it, and has made fighting fare evasion a top priority, but he can’t turn it around on his own.

That requires action by cops, prosecutors, courts and lawmakers.

Meaning more arrests, more prosecutions and convictions — and smartly toughened laws.

New York’s political class knows how to bring crime down: The city’s done it before.

If the politicians refuse, it’s up to the voters to elect new ones.