Police say a 3-year-old girl was found dead in her mother's arms in Bed-Stuy early this morning. Authorities say they received a 911 call about a possible jumper on the roof of 1078 Putnam Ave. at around 4 a.m. No one was on the roof when they arrived, but a blood trail led them to an open apartment where they say the child was found bleeding with her mother. Investigators say the girl had several cuts and injuries to her face and neck, but have not yet confirmed how she died. Police say the mother was incoherent and babbling when they arrived, and is now undergoing psychiatric evaluation at Woodhull Hospital.