Gilbert Arenas -- Arrested for Truckload of Illegal Fireworks

6:45 AM PT Arenas was booked for misdemeanor possession, and has been released without bail. We're told there were 100 POUNDS of fireworks in the truck.

Ex-NBA star Gilbert Arenas' 4th of July is gonna suck -- 'cause he got nailed by cops early this morning for illegal fireworks -- A TON OF ILLEGAL FIREWORKS -- as in a full truckload of 'em ... TMZ has learned.

Law enforcement sources tell us Arenas was pulled over by California Highway Patrol around 2:30 AM in Los Angeles for speeding in a Ford pickup -- but officers immediately saw that the truck was filled with fireworks ... sitting in plain sight in the bed and cab of the truck.

We're told Arenas was arrested and will be booked for possession of illegal fireworks, and cited for speeding -- he was allegedly doing 80 mph -- and driving without a license.

It's unclear exactly how much fireworks were in the truck, but it was enough that the LAPD bomb squad was called to handle the illegal booty.

Our camera guy counted around 20 boxes being unloaded ... very carefully.

Arenas -- whose last NBA team was the Memphis Grizzlies in the 2011-12 season -- was infamously busted for gun possession when he brandished a loaded pistol in his Washington Wizards locker room back in 2010.