Protesters are welcome to picket Times Square on New Year's Eve, but should expect to arrive long before the ball drop, the NYPD said Tuesday.

Thousands of uniformed and plainclothes cops -- including all the recruits who graduated Monday -- are to police the event, expected to attract more than 1 million celebrants.

Asked about protesters joining the world's premier New Year's celebration, NYPD Chief of Department James P. O'Neill said: "The pens fill up early. I mean, this is a long day. You know, people start getting there very early in the morning, so, unless you get there real early, you're probably not going to get close to the stage."

Added the NYPD's counterterrorism boss John Miller, "Once they're closed, they're closed. People are free to leave. It's going to be hard to get back in, and I think the protesters will have to deal with that."

O'Neill said the NYPD would have additional personnel in case of protests.

A group called Stop Mass Incarceration, for example, plans a 10 p.m. march to Times Square to "Rock in the New Year With Resistance to Police Murder!"

Protesters would be subject to the same restrictions as everyone else, such as a limit on the size of bags and coolers, though placards aren't banned, O'Neill said.

The city has been beset with protests this month over a grand jury's decision not to indict a cop in the chokehold death of Eric Garner.

"Our policing philosophy is going to remain consistent," O'Neill said. "People have an absolute right to protest still, and as long as they do it peacefully and laws aren't broken, that's the way we're going to police the event."

The evening is to be monitored by choppers, chemical and radiological detectors, mounted units, scooters and foot patrol.