Mayor Bill de Blasio got the hoped-for national headlines with his rollout Tuesday of “universal” health care. But the reality is barely more than a con job, albeit one likely to mean trouble for taxpayers down the line.

“We’re going to guarantee health care” for all New Yorkers, regardless of immigration status or ability to pay, he boasted. But the city already does that.

Anyone who lacks insurance and can’t afford health care, including illegal immigrants, can walk into any of the city’s Health + Hospitals facilities right now.

His initiative merely adds to the marketing for the city’s current “public option” health insurance, MetroPlus, while also boosting a “customer service” feature to steer people to H+H clinics. That’s how de Blasio can aim to ultimately “help” 600,000 New Yorkers (including 300,000 illegal immigrants) who lack insurance at a cost of $100 million a year — about $167 per head.

Yet taxpayers are at risk for bigger bills: Programs like this are infamous for busting past projected costs. If word of “guaranteed health care” lures out-of-towners (and out-of-countriers) here, costs could soar. And the mayor’s hope for “savings” — moving people to get care before they need expensive emergency room visits — has been the goal of reforms for decades now.

Yes, once-cash-strapped H+H’s finances are, for now, OK. But that’s largely because he has been bailing it out, to the tune of billions a year — money the city can spare as long as the economy stays strong. And the agency is already at risk of slipping deeply into the red within another couple of years.

If de Blasio expects this to burnish his national progressive reputation, he has a darn low opinion of his fellow travelers’ IQ.