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