Vice President Joe Biden on Sunday basically branded Mayor Mike a liar over the latter’s claim that holding those misguided 9/11 terror trials in Lower Manhattan would nick the city for $200 million a year in security costs.

And, so far, Bloomberg is letting him get away with it.

“The mayor came along and said the cost for providing security to hold this trial is X hundreds of millions of dollars, which I think is much more than would be needed,” said Biden — that world-renowned estimator of terror-trial costs.

Not.

Certainly, given the unknowns — and the unknowables — involved in such things, no one can say for sure what the final cost will be.

But Police Commissioner Ray Kelly, who drew up the plans for trial security, is doubtless far better situated than Joe Biden to offer an estimate.

Queens Councilman Peter Vallone Jr. stated the obvious: “Our police commissioner is perhaps one of the world’s foremost experts on public safety, and Joe Biden treads on dangerous waters when he believes he knows more about the safety of New York City.”

Only two things could explain Biden’s presumption: Either he really is that dense (always a possibility) — or he’s saying Bloomberg and Kelly are liars.

What we don’t get is why Mike is putting up with it. He really needs to call Biden out on this — publicly.

Too bad dueling is out of style.