INTERIM MAINTENANCE: Following completion of AZACITIDINE BLOCK II, patients receive mercaptopurine PO or NG daily on days 1-14, methotrexate IV over 24 hours on days 1 and 8 and IT on days 2 and 9, hydrocortisone sodium succinate IT on days 2 and 9, leucovorin calcium PO or IV on days 2-3 and 9-10, cytarabine IV over 3 hours every 12 hours on days 15-16 and 22-23 for a total of 8 doses, and pegaspargase IV over 1-2 hours or IM on day 23 in the absence of disease progression or unacceptable toxicity.