DISEASE CHARACTERISTICS: Acute leukemias in the following categories: Histologically documented ANLL in first remission (CR1) or second remission (CR2) Pediatric ANLL patients in CR1 eligible provided they are not enrolled on protocol CCG-2891 ALL in CR1 presenting with at least 1 of the following high-risk features: WBC at presentation greater than 50,000/mm3 (200,000/mm3 in pediatric patients) Hypoploidy as measured by flow cytometry Pseudodiploidy with translocations t(9;22), t(4;11), and t(8;14) CR not achieved until after 4 weeks of induction therapy ALL in CR2 that has relapsed in the bone marrow following a first remission regardless of time of relapse Acute biphenotypic leukemia (mixed myeloid and lymphoid lineage at presentation) in CR1 or CR2, i.e., patients classified as lymphoblastic or myeloblastic based on FAB morphology and histochemistry features Adult acute undifferentiated leukemia (no evidence of lymphoid or myeloid differentiation) and in CR1 or CR2 Patients in this category are analyzed separately CR defined as no evidence of leukemia at time of transplantation as documented by normocellular bone marrow aspirate containing no more than 5% blasts no more than 2 weeks prior to cytoreduction Normal diagnostic LP or Ommaya reservoir tap required no more than 2 weeks prior to start of cytoreduction in all ALL patients and in ANLL patients at risk for CNS disease No extramedullary disease at time of transplantation HLA-identical, MLC-compatible related donor required Donor must be healthy and willing to undergo general anesthesia and donation procedure For T-cell depletion, donor should be able to have a volume of 15 ml/kg patient body weight harvested safely