Chemotherapy Plus Interferon Alfa Alone or With Radiation Therapy and Peripheral Stem Cell Transplantation in Treating Patients With Stage III or Stage IV Follicular Non-Hodgkin's Lymphoma

RATIONALE: Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. Interferon alfa may interfere with the growth of cancer cells. Radiation therapy uses high-energy x-rays to damage cancer cells. Peripheral stem cell transplantation may allow the doctor to give higher doses of chemotherapy drugs and radiation therapy and kill more cancer cells. PURPOSE: Randomized phase III trial to compare the effectiveness of combination chemotherapy followed by interferon alfa alone or combination chemotherapy plus radiation therapy and peripheral stem cell transplantation in treating patients who have previously untreated stage III or stage IV follicular non-Hodgkin's lymphoma.