1. FOR PHASE I COMPONENT OF THE STUDY: Patients with refractory or relapsed: acute myelogenous leukemia (AML), acute lymphocytic leukemia (ALL), and myelodysplastic syndrome (MDS) are eligible. Patients with chronic lymphocytic leukemia (CLL) are eligible if fludarabine based therapy has failed. Patients with chronic myeloid leukemia (CML) are eligible if they have documented hematologic resistance to imatinib mesylate or have not achieved or lost any cytogenetic response to imatinib mesylate after 12 months of therapy.