OBJECTIVES: I. Determine whether event-free survival for children with T-cell non-Hodgkin's lymphoma (NHL) can be improved by the addition of a third intensification block at 35 weeks. II. Determine biology and treatment response of T-cell NHL and T-cell acute lymphocytic leukemia when both are treated with an identical leukemia type protocol and receive a third intensification block. III. Improve the outcome for the 25% of children who are not in remission at eight weeks by the addition of a block of sustained intensification before high dose methotrexate and continuing treatment.