11:13 AM PT -- Jessica Peet tells TMZ ... "I want to apologize for what I posted as a 14-year-old teenager. In no way did I mean it in a derogatory nor racial way. I do hope people are willing to forgive, and understand I was immature and I've done a lot of growing up since then."

One of the 'Survivor' contestants from the upcoming season is catching heat before the show even airs ... for using the n-word so much on Twitter, you'd think she was Jay-Z.

19-year-old Jessica Peet is a cast member on "Survivor: David vs. Goliath" and, as it always does ... the Internet scoured her social media, and turned up scores of old tweets where she gratuitously drops the n-word.

She even defends using it, saying, "n***a isn't a cuss word !! Lol" -- and, in another, adds ... "I have a way with words..... N***a." Indeed.

The tweets, which 'Survivor' fans grabbed before they were deleted, are from 2013 to 2015. Many fans online are calling Peet a racist.

Sources close to the production tell TMZ ... CBS is aware of the situation, and Peet apologized by saying she was "young and dumb." She would've been between 14 and 16 at the time.

This drama comes on the heels of a pair of upcoming contestants getting into hot water for breaking their NDAs by posting a pic together ... before CBS revealed the cast.