A Black screenwriter is blaming an "old white lady" for getting him kicked off a train ... he says he was racially profiled, but cops in New York say he refused to take his feet off a seat.

Alex O'Keefe , who writes for the FX hit "The Bear," posted video of himself being confronted by MTA police officers while on a train from NYC to Connecticut ... and he says a "Karen" complained and told him "to correct how I was sitting."

The video shows cops slapping handcuffs on Alex and hauling him off the train. He's being told to stop resisting and he asks officers if he's being arrested. Alex turns the camera on an elderly white woman in a face covering, who he says pointed at him when she got on board.

Alex claims he was arrested but the MTA Police Department says he was NOT busted ... and w

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