Keanu Reeves is going to bat for a director convicted of defrauding Netflix out of $11 Million ... and you can read the letter the actor sent to a federal judge, where Keanu asks for a light sentence for his friend.

Keanu's letter was part of a sentencing memorandum in the case of Carl Rinsch, who was convicted in December on federal charges including wire fraud and money laundering.

Prosecutors claimed he used Netflix money intended for a series called "White Horse" and used it to fund a lavish lifestyle.

In Keanu's letter, he says Carl became a friend after directing him in the 2013 movie "47 Ronin" and that Carl can “self-sabotage" by pushing boundaries.

Keanu also mentions "White Horse" ... he says Carl showed him the project back in the day when it was still unfinished, describing it as a "superb and visionary art."

Carl gets a glowing review from Keanu, hailing him as an "exceptional artist" who brings joy, warmth and creative inspiration to others.

The judge is set to sentence Carl on June 29 ... and it will be interesting to see if Keanu's letter moves the needle.

Stay tuned ...