DISEASE CHARACTERISTICS: Acute myelocytic leukemia with or without history of myelodysplastic syndrome Not in first complete remission (i.e., greater than 5% blasts in marrow) with t(8;21), t(15;17), or 16q abnormality unless failure on first-line induction therapy Acute lymphocytic leukemia (ALL) in one of the following categories: In second or third complete remission (CR) High-risk ALL in first CR, with high risk defined as: Hypodiploidy OR pseudodiploidy with t(9;22), t(4;11), or t(8;14) Failure to achieve CR after 4 weeks of induction therapy Elevated WBC at presentation, i.e.: Greater than 100,000 in patients aged 6 to 12 months Greater than 200,000 in patients aged 1 to 20 years Greater than 20,000 in patients aged 21 to 44 years Chronic myelogenous leukemia not in blast crisis (i.e., no greater than 30% promyelocytes plus blasts in bone marrow) Stage IV lymphoblastic lymphoma Undifferentiated or biphenotypic leukemia Unrelated donor available Patients aged 35 and younger: HLA-A, and -B serologic identity and HLA-DRB1 identity by high-resolution DNA typing OR Single HLA-A or -B serologic mismatch with DRB1 identity by high-resolution DNA typing OR HLA-A and -B serologic identity with single DRB1 mismatch by high- or low- resolution DNA typing Patients aged 36 to 44: HLA-A and -B serologic identity and HLA-DRB1 identity by high-resolution DNA typing The following exclude: Relapse 12 months after discontinuing therapy in patients aged 1 to 10 years who are in second remission Active central nervous system or leukemic skin involvement Requirement for additional mediastinal irradiation