'American Idol' -- Bikini Girl Katrina Darrell ARRESTED for DUI

Katrina Darrell -- the chick who famously auditioned for "American Idol" in a bikini back in 2009 -- was arrested this morning for DUI ... TMZ has learned.

According to Pomona PD Sgt. Patrick O'Malley, the 24-year-old singer ... also known as "Bikini Girl" ... was arrested in Los Angeles at 12:16 AM ... with her mother in the passenger seat.

Darrell allegedly told police she was en route to a nearby hospital ... because her mom had fallen down at home.

But while Katrina was driving to the hospital, she allegedly ran a red light and smashed into another vehicle.

Darrell allegedly tried to flee the scene ... but a nearby officer who heard the crash responded and pulled over Katrina's 2004 Toyota Camry.

When the officer approached Katrina, he smelled booze ... and gave her a field sobriety test. She performed poorly ... and was arrested for DUI.

Katrina -- who was crying hysterically during the arrest -- was hauled to a nearby police station ... where she took a breathalyzer test ... and blew a .15 and a .17 ... WAYYYY over the legal limit, .08.

Katrina was eventually cited and released just after 6AM. As for her mom, an ambulance was called to the scene of the arrest ... but her condition is unclear.

Things could get worse for Katrina ... we're told she could also face charges for hit and run for allegedly trying to flee the scene of the initial accident.