9:17 AM PT -- A source close to O.T. Genasis tells TMZ the dispute was over his ID and another rapper's ID. We're told at no time did any member of his crew pull out a gun or make any threats.

Who needs ID when you've got a gun?

O.T. Genasis rolled deep to The Good Nite bar in the San Fernando Valley early Thursday morning. We're told O.T. and his crew arrived after 1 AM with a bunch of girls, pushed past the bouncer and headed straight to the bar. Things got HEATED when the bartender asked the chicks for ID, and then --- according to cops -- out came the blue steel.

Law enforcement sources and eyewitnesses tell us ... someone in O.T.'s crew pulled out a gun and threatened to shoot up the place. The bartender snapped some pics, and that got the gunman pissed and he tried smashing the phone.

Police were called but, by the time they arrived, O.T. and his boys were gone. Police are investigating what could be a felony -- making criminal threats along with brandishing a weapon.

It's the 2nd time this summer cops have been called on O.T. and co. because of alleged gun threats.

As we reported ... O.T.'s birthday celebration at a bowling alley was swarmed by police after a reported gun threat.