MIKE Bloomberg needs to ignore apocalyptic rhetoric – publicly and emphatically, if possible, but ignore it nevertheless.

Teachers going to run off to Westchester if they don’t get a 25 percent raise – and then the schools will collapse?

Let ’em run. And good luck to them, because Westchester isn’t hiring in numbers that New York needs to fret over.

And if the schools collapse – well, how could anybody tell?

Cops going to bail out for Suffolk County – the promised land of high pay and harmless perps – and then a crime wave will crest over Gotham?

Suffolk, sadly for the cops, isn’t hiring either. Not enough to make a difference.

Thus the cops are stuck. And so are the teachers.

And you know what?

They’ll do their jobs, just like they always do, because they have no real choice and they know it. And because, by and large, they are professionals.

So there’ll be no crime wave, either.

And the schools will be – well, the schools.

Presently a vagrant will be found dead in the cold, and this quiet tragedy will be cited, unquietly, as proof both of the hard-heartedness of Bloomberg’s predecessor and of the cruel inadequacy of the city’s “homeless” policies.

It will be rank nonsense, of course – the city spends gazillions on “affordable” housing, and it’s the civil-liberties zealots who stand between helpless, mentally ill street people and a warm bed.

But sound bites and video clips have lives of their own in the continuing struggle to separate taxpayers from their money on behalf of dubious social programs – and a new mayor must always be tested.

And this one will be, in many ways.

That’s why, when the advocates predict Armageddon, Mike Bloomberg needs to say: “Is that so? Prove it!”

Of course, they never can.

Bob McManus is The Post’s editorial-page editor.