11:15 AM PT -- A close friend of the Baldwins tells TMZ ... Alec was in the park with his wife Hilaria and their baby when a paparazzo approached them. According to the friend, Baldwin has some history with the photog -- he's allegedly called Hilaria a bitch and a whore in the past -- which is why Alec immediately got so angry.
A cop who was nearby tried to calm things down, but felt he needed backup ... it was Alec Baldwin, after all.
We're told one of the responding officers successfully cooled down the situation -- and even got Alec and the photog to shake hands before they walked away!
Alec Baldwin got very angry this morning in the Hamptons, and there was an immediate show of force from the local police department.
In the video, shot in East Hampton ... Alec is on a sidewalk talking to two police officers. His voice is raised, but it's hard to make out why he's pissed.
Whatever it was ... it was serious enough that THREE other patrol cars quickly rolled up with their sirens blaring. Toward the end of the clip. you can hear Alec yell, "I want this man arrested!"
It's unclear what got Baldwin so heated, or who he wanted tossed in jail.