DISEASE CHARACTERISTICS: Histologically confirmed malignancy Acute myeloid leukemia (AML) Complete remission 1 (CR1): high risk defined by poor cytogenetics (e.g., deletions, additions, or multiple abnormalities) Complete remission 2 (CR2) Induction failures Relapse: at least one reinduction attempt if at least 10% marrow blasts Acute lymphocytic leukemia CR1: high risk defined by overt CNS involvement or poor cytogenetics (e.g., additions, deletions, translocations, or multiple abnormalities) CR2 Induction failures Relapse as for AML Chronic myelogenous leukemia Chronic phase (CP) 1 Accelerated phase (AP)/CP2: blast phase patients require induction and achievement of a second chronic phase prior to transplantation Chronic lymphocytic leukemia Relapse: any stage and must have received no greater than 3 regimens since diagnosis Multiple myeloma Primary refractory disease at diagnosis Relapse (no greater than 2): sensitive disease Plasma cell leukemia Inability to achieve a complete remission or relapse after autologous transplantation (no greater than 40 years) Myelodysplasia All FAB subtypes Myeloproliferative disorders Poor response to medical therapy OR Cytogenetic abnormalities Severe aplastic anemia (SAA) (for unrelated and/or mismatched donors) Very SAA at diagnosis OR SAA: induction failures One antigen mismatch (recipient age 15 to 55) Related donors may be A, B, or DR mismatched Unrelated donors may be A or B mismatched (DRB1 match) Phenotypic (6 out of 6) match Recipient age 51 to 60 if related donor Recipient age 41 to 55 if unrelated donor