Just three weeks before NYU’s newest class moves into the area, a group of junkies and crackheads has turned a leafy pathway in Washington Square Park into an open-air drug den — and the NYPD is doing nothing about it.

As many as 20 strung-out vagrants have taken over several benches in the park’s northwest corner, where they openly consume hard drugs just steps from the children’s playground, outraged neighbors said.

One Village resident who walks his dog through the park daily said he has repeatedly witnessed people blatantly smoking crack — and even saw one man use a handheld mirror to inject narcotics into a vein in his neck as two cops sat in a cruiser about 15 feet away.

“I dunno if they have a Twitter feed or what, but the word is out and the numbers get bigger by the day,” said the resident, a 33-year-old property manager.

“I’ve lived by the park seven years and I have never in my life seen someone shooting heroin in the middle of broad daylight, literally surrounded by pedestrians enjoying an afternoon outside.”

Village resident Martin Felondo, 53, said he recently complained to a cop about being harassed by a dealer who followed him through the park, trying to sell him drugs.

“The cop just told me to calm down,” Felondo said.

Felondo also noted that he has frequented the park since 1987, adding: “I’ve seen trends come and go, and I’m not too keen on what’s going on with heroin.”

Will Falzon, who works as a building super nearby, said the situation was “really a safety concern, more than anything.

“The quality of people coming here and participating in that kind of activity aren’t the kind of people that a residential neighborhood needs. It’s not what you want to see,” said Falzon, 57.

Thursday afternoon, The Post spotted three people firing up a glass stem and puffing away on benches in the area.

Afterward, none would discuss what they had been doing.

About a half-dozen other apparent druggies were seen shuffling around like zombies and occasionally spewing curses at each other.

One man urinated on a tree.

A Parks Department worker admitted that he and his colleagues had quit cleaning up the area because they were scared of the addicts.

“There’s drug use, prostitution, gambling — all that is going on there. All day and all night, too,” the worker said.

“In that area over there, though, it’s off the chain and the cops know what’s going on. I ain’t touching that situation. That’s on them.”

No cops were stationed inside the park Thursday, but at one point, two officers pulled up in a patrol car and parked at Washington Square North to eat ­salads in their vehicle.

Asked why they weren’t cracking down on the lawlessness within their sight, one cop said: “We aren’t even here for that specifically. There’s a unit that’s dealing with all of that. I can’t say more than that.”

They left about 10 minutes later.

An NYPD spokeswoman, Sgt. Jessica McRory, said: “The precinct has received complaints in regards to that area of the park. We currently have officers assigned to that area.

“The commanding officer [Deputy Inspector Joseph Simonetti] has contacted narcotic investigators to address the condition.”

Only weeks ago, dozens of druggies zonked out on K2 were found staggering around the streets of Brooklyn: