Cytarabine and Clofarabine in Treating Patients With Refractory or Relapsed Acute Myeloid Leukemia or Acute Lymphoblastic Leukemia

DISEASE CHARACTERISTICS: * Pathologic confirmation of acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL) * No M3 AML * Meets 1 of the following criteria: * In first relapse * In second relapse after a second complete remission (CR) that lasted ≥ 3 months * Refractory to initial induction therapy * No symptomatic CNS involvement PATIENT CHARACTERISTICS: * ECOG performance status ≤ 2 * Creatinine \< 2 mg/dL * Bilirubin ≤ 2 mg/dL * AST and ALT ≤ 4 times upper limit of normal * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 2 weeks after completing study treatment * Ejection fraction ≥ 45% by echocardiogram * No active, uncontrolled systemic infection considered opportunistic, life-threatening, or clinically significant * No psychiatric disorders that would interfere with giving consent, study participation, or follow-up procedures * No other severe concurrent disease that would preclude study treatment PRIOR CONCURRENT THERAPY: * At least 1 week since prior therapy and recovered * No other concurrent chemotherapy * Hydroxyurea to control WBC count before starting study treatment allowed * No concurrent corticosteroids unless used for diseases other than leukemia * No concurrent palliative radiotherapy * No concurrent growth factors (e.g., epoetin alfa, filgrastim \[G-CSF\], or sargramostim \[GM-CSF\]) in patients with AML