An Orthodox Jewish construction manager — and NYPD clergy liaison — was stabbed Monday as he sat in traffic on a busy Brooklyn Heights street, witnesses and sources said.

Yaakov Pfieffer, 30, had just gotten in his truck and was idling near a construction site at 172 Montague St. just after 1 p.m. when a disgruntled worker ran up and stabbed him through the driver’s side window, according to the witnesses and sources.

Tim Woods, 49, who was working on a film shoot near the scene, saw the victim stumble out of his white Dodge Ram with blood spurting out of his neck, screaming, “Somebody help me! Call 911!”

“By that time, he started running down the street and collapsed,” Woods said. “Three other drivers saw the truck rolling into a crosswalk so we all ran and tried to stop [it].”

Alex Kwong, 24, said he and his passenger saw the stabber running away as he tried to stuff the bloody 6-inch blade into the pocket of his filthy blue jeans.

“The most dramatic part was we see the guy jump out of his car and stand in the street, blood everywhere,” Kwong said.

Several people rushed to help Pfieffer and others chased the suspect. They pinned him against the side of a TD Bank and held him until police arrived and busted him.

One of the men managed to wrestle the knife out of his hand.

“They asked him, ‘Why did you stab that man?’ ” said witness Avi Navon. “He said, ‘I worked two weeks for this guy and he hasn’t paid me. That’s the reason I did what I did.’ ”

The suspect Andriy Komynar, 20, was arrested at the scene and later charged with assault.

Komynar is a Ukraine native who was hired by Pfieffer to do electrical work.

Pfieffer, a clergy liaison between the NYPD and the Orthodox community, underwent surgery at Lutheran Hospital and was expected to survive.