Combination Chemotherapy in Treating Children With Acute Lymphoblastic Leukemia, Osteosarcoma, or Non-Hodgkin's Lymphoma

DISEASE CHARACTERISTICS: * Histologic evidence of one of the following malignancies that has failed conventional therapy: * Acute lymphoblastic leukemia * Non-Hodgkin's lymphoma with bone marrow involvement * Osteogenic sarcoma * In vitro transport resistance to methotrexate demonstrated by bone marrow aspirate assay PATIENT CHARACTERISTICS: Age: * 21 and under at diagnosis Performance status: * ECOG 0-2 Life expectancy: * At least 8 weeks Hematopoietic: * Granulocytopenia allowed with bone marrow involvement * Thrombocytopenia allowed with bone marrow involvement * Anemia allowed with bone marrow involvement Hepatic: * (unless due to disease) * Bilirubin no greater than 2.0 mg/dL * AST no greater than 100 Renal: * Creatinine less than 1.5 mg/dL OR * Creatinine clearance at least 60 mL/min Other: * No other serious medical illness * Not pregnant or nursing * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: * Prior bone marrow transplantation allowed Chemotherapy: * At least 1 week since prior intrathecal treatment * At least 2 weeks since prior systemic chemotherapy and recovered * At least 10 days for rapidly proliferating leukemia (i.e., WBC greater than 50,000) * No concurrent chemotherapy Endocrine therapy: * Not specified Radiotherapy: * Prior radiotherapy allowed and recovered * No concurrent radiotherapy Surgery: * Not specified