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

DISEASE CHARACTERISTICS: * Histologically confirmed diagnosis of 1 of the following: * Acute myeloid leukemia (AML) with ≥ 5% blasts in the bone marrow (M2/M3 bone marrow) with or without extramedullary disease * Acute lymphoblastic leukemia (ALL) with \> 25% blasts in the bone marrow (M3 bone marrow) with or without extramedullary disease * Acute leukemia of ambiguous lineage with ≥ 5% blasts in the bone marrow (M2/M3 bone marrow) with or without extramedullary disease * Disease must have relapsed after or be refractory to prior induction therapy * Patients with AML or acute leukemia of ambiguous lineage must be in first relapse OR refractory to first induction therapy with ≤ 1 attempt at remission induction * Patients with AML who enroll on the phase I portion of the study must have received prior mitoxantrone hydrochloride and cytarabine for newly diagnosed AML (phase I closed to accrual as of 09/16/09) * Patients with ALL must be in second or third relapse (≤ 3 prior induction regimens) OR refractory to reinduction in first relapse * Patients with ALL refractory to first induction therapy are not eligible * No acute promyelocytic leukemia * No CNS 3 involvement (i.e., WBC ≥ 5/μL in the cerebrospinal fluid with blasts present on cytospin) PATIENT CHARACTERISTICS: * Karnofsky performance status (PS) 50-100% (\> 16 years of age) OR Lansky PS 50-100% (≤ 16 years of age) OR ECOG PS 0-2 * Life expectancy ≥ 8 weeks * Creatinine clearance or radioisotope …