In what has to be one of the more polite recent NYPD arrests, a Brooklyn ex-convict alerted two patrol cops that he was carrying a loaded pistol — and they thanked him before slapping on cuffs.

Lawrence Johnson was nervously chatting on a cellphone at Blake Avenue and Warwick Street in East New York on Nov. 4 when a police cruiser pulled over.

Johnson “stepped into the street toward the police ­vehicle,” and one of the cops asked if he needed something, according to a criminal complaint filed in Brooklyn federal court.

“The defendant looked down at the gun case in his left hand and stated, ‘I have a gun,’ ” the complaint says.

One of the cops “observed that on the side of the gun case was written the words ‘Gun Guard.’ ”

The cop “thanked the defendant for advising [him] that he had a firearm,” and the officers proceeded to arrest him, the complaint says.

They recovered a .45-caliber semiautomatic pistol with a magazine containing eight rounds, according to the complaint.

Johnson was charged with a federal gun-possession rap because of his long history of prior felonies.