EXCLUSIVE

Everyone knows you NEVER BRING A LOADED GUN TO AN AIRPORT ... everyone, except Dwight Howard apparently.

TMZ Sports has learned the NBA superstar was stopped at George Bush Airport in Houston on August 28th ... when Dwight put his carry-on bag through the scanner, and a TSA agent noticed a LOADED GLOCK inside!!!

Law enforcement sources tell us ... a further inspection revealed the gun -- a Glock 26 9mm -- was LOADED with one round in the chamber.

We're told Dwight said he simply forgot the gun was in the bag.

But multiple law enforcement sources tell us ... because it's Texas -- and they have looser gun laws than states like California -- Dwight was NOT ARRESTED.

Cops were called to the scene, but we're told he was allowed to give the weapon to an associate who took the gun out of the airport.

As for Dwight, once he was disarmed -- he was allowed to get back in the security line ... and boarded his plane as if nothing ever happened!