CONSOLIDATION THERAPY** (ALL PATIENTS): Beginning on day 36 (after completion of induction therapy) or after completion of extended induction therapy, patients (RER and SER) receive cyclophosphamide IV over 30 minutes on days 1 and 29; cytarabine IV or SC on days 1-4, 8-11, 29-32, and 36-39; mercaptopurine PO on days 1-14 and 29-42; vincristine IV on days 15, 22, 43, and 50; study drug IV over 1 hour on days 15 and 43; and methotrexate IT on days 1, 8, 15*, and 22*. Patients then proceed to interim maintenance I therapy.