Michael Phelps -- Arrested FOR DUI ... Again

Michael Phelps was arrested for driving under the influence in Baltimore, Maryland early this morning ... TMZ Sports has learned.

Our sources tell us ... the USA Olympic legend was pulled over around 1:40 AM in his white Land Rover. We're told he bombed his field sobriety test ... and his B.A.C. was almost twice the legal limit.

Officials just issued a statement saying Phelps was initially pulled over for going 84 in a 45 ... and during the stop, the officer noticed he was hammered.

Our sources say Phelps was hauled to a nearby station where he was booked for DUI -- and was eventually released.

Cops say Phelps was charged with DUI, excessive speeding and crossing double lane lines.

It's Michael's 2nd DUI arrest -- he was popped in Maryland in 2004 when he was 19 years old. He struck a plea deal with prosecutors and pled guilty in exchange for 18 months probation.

We've made multiple calls to Michael's reps -- but they would not take our calls.

1:00 PM PT -- Michael is now apologizing for the arrest.