Ex-NBA star Gilbert Arenas has been charged with a crime for transporting more than 100 pounds of dangerous fireworks right before the 4th of July ... and could face serious jail time TMZ has learned.

We broke the story ... Arenas was pulled over by the California Highway Patrol on June 27 for speeding ... and during the bust cops say they found more than 100 pounds of fireworks.

Arenas was arrested -- and now we've learned he's been charged with misdemeanor possession of dangerous fireworks without a permit.

Law enforcement tells TMZ ... because he had more than 100 pounds of bang bang he faces up to 1 year in county jail and up to $10000 in fines.