Paris Jackson -- My Uncle Randy Is a BIG, FAT LIAR

Michael Jackson's only daughter is going to war with one of her famous uncles ... claiming Randy Jackson is spreading dangerous lies about the family ... and she's calling him out in public.

It's all over a letter that supposedly "leaked" to the Internet this week ... in which Randy, along with Jermaine, Janet, Tito and Rebbie demand John Branca and John McClain resign from their positions as the executors of the Michael Jackson Estate, effective immediately.

In the sharply-pointed letter, the family claims Branca and McClain have "failed" in their duties ... taken advantage of the family ... and have stressed out Katherine Jackson so much, that she recently suffered a "mini-stroke."

Randy went to Twitter and verified the authenticity of the letter Tuesday night ... but the very next day, Paris called BS on her uncle.

In fact, the 14-year-old went to her own Twitter page ... and wrote, "i am going to clarify right now that what has been said about my grandmother is a rumor and nothing has happened , she is completely fine."

She added, "i'd like to know who made up the rumor… i will defend my beloved family member with all i have , even if it means from other family members.”

Minutes later, Paris sent a new message directed to Randy -- which said, "@randyjackson8 hello dear FAMILY member i don't appreciate you telling everyone things that aren't true thank you very much."

When one of her followers suggested Paris should have respect for Randy ... she replied, "Maybe he should have respect for his mother."