Combination Chemotherapy Followed by Peripheral Stem Cell Transplantation in Treating Patients With Chronic Myelogenous Leukemia or Myelodysplastic Syndrome

DISEASE CHARACTERISTICS: Diagnosis of chronic myelogenous leukemia (CML) (BCR/abl or Philadelphia (Ph) chromosome positive) Accelerated phase More than 10% and less than 30% myeloblasts and promyelocytes in marrow or peripheral blood Perturbations of white count, platelet count, or hematocrit uncontrolled by chemotherapy with busulfan or hydroxyurea Progressive splenomegaly refractory to chemotherapy Extramedullary tumor Presence of a nonconstitutional cytogenetic abnormality in addition to a single Ph chromosome, except for -Y Persistent unexplained fever or bone pain Blast phase More than 30% myeloblasts and promyelocytes in marrow or peripheral blood Remission after blast phase Less than 10% blasts in marrow and peripheral blood with a history of blast phase Any phase of CML if there is a contraindication to conditioning therapy with cyclophosphamide OR Diagnosis of myelodysplastic syndrome (MDS) with any of the following subtypes: Refractory anemia (RA) or RA with ringed sideroblasts (RARS) High-risk cytogenetics (i.e., monosomy 7 or complex abnormalities) RA with excess blasts (RAEB) Presence of 5-20% blasts in marrow and less than 5% blasts in peripheral blood RAEB in transformation 21-30% blasts in marrow OR more than 5% blasts in peripheral blood Chronic myelomonocytic leukemia Presence of no more than 20% blasts in marrow, less than 5% blasts in peripheral blood, and more than 1,000 monocytes/uL of peripheral blood Secondary acute myeloid leukemia arising from pre-existing MDS More than 30% blasts in marrow Any stage of MDS if there is a contraindication to conditioning therapy with cyclophosphamide Related or unrelated donor compatible for HLA-A, B, C, DRB1, and DQB1 antigens Mismatch for a single HLA-A, B, C, DRB1, and DQB1 allele within the same broad serotype (e.g., A*0101 vs 0102) or crossover group (e.g., A*0101 vs 0301) allowed PATIENT CHARACTERISTICS: Age: 65 and under Performance status: Not specified Life expectancy: Not severely limited by diseases other than malignancy Hematopoietic: See Disease Characteristics Hepatic: No hepatic disease AST no greater than 2 times normal Renal: Creatinine no greater than 2 times normal OR Creatinine clearance at least 50% for age, weight, and height Cardiovascular: No cardiac insufficiency requiring treatment No symptomatic coronary artery disease Pulmonary: No severe hypoxemia (pO2 less than 70 mm Hg and DLCO less than 70% predicted) No mild hypoxemia (pO2 less than 80 mm Hg and DLCO less than 60% predicted) Other: HIV negative Not pregnant or nursing PRIOR CONCURRENT THERAPY: See Disease Characteristics No concurrent growth factors during methotrexate administration