Law enforcement sources tell us police got a call around 1AM that someone was brandishing a gun at Supper Club ... and when officers arrived on scene a witness identified Katt as the suspect.

We're told police did not find a gun on Katt, but when they found one in his car -- Katt and two other members of his entourage were taken into custody for questioning.

Police have since released one of the men, and booked another on an unrelated traffic warrant.

We're told the gun was unregistered and police are trying to find out who owns it.