OUTLINE: This is a multicenter, phase I, dose-escalation study of clofarabine followed by an randomized phase II study. Patients are stratified according to center, and presence of poor prognostic features (WBC at diagnosis ≥ 100,000/μL vs presence of very high risk cytogenetic features -5/5q-, -7/7q-, presence of complex abnormalities [> 3 abnormalities], 3q, t[6;9], or t[9;22]). Patients are randomized to 1 of 2 treatment arms.