Sophie Stack Lachman;of 414 Fayette St.;Belle Vernon;died Tuesday;March 31;1981;at 12:40 a.m.in Montefiore Hospital;Pittsburgh.   She was 71.  Mrs.Lachman was born April 13;1909;in Charleroi;a daughter of the late Frank and Mary Kijowski Stack.  A life-long resident of the Belle Vernon Area;she was a member of St.Sebastian R.C.Church;Belle Vernon;and the Ladies’ Guild of the church;and the Catholic Daughters of America Belle Vernon Court 1522.  She was preceded in death by two brothers;John and Michael Stack.  Survivors include her husband;Joseph W.Lachman;at home;two sons;Joseph J.Lachman of Fairhope and William A.Lachman of Bulger;Pa.;a daughter;Mr. Leonard (Loretta) Cardiff;of Irwin;Pa.;three brothers;Stanley Stack and William Stack;both of Donora;and Anthony Stack of Modesto;Calif.;a sister;Mrs.John (Stella) Janney;of Donora;and nine grandchildren.  Friends will be received at the Leonard J.Parzynski Funeral Home;626 Broad Ave.;Belle Vernon;Tuesday from 7 to 9 p.m.and Wednesday from 2 to 4 p.m.and 7 to 9 p.m.  A Parish Wake Service will be held Wednesday at 8:30 p.m.in the funeral home.  A Prayer Service will be held Thursday at 9:30 a.m.in the funeral home;followed by a 10 a.m.Mass of Christian Burial at St.Sebastian R C.Church;Belle Vernon.  Burial will be in Belle Vernon Cemetery.  The Leonard J. Parzynski Funeral Home is in charge of arrangements.