RATIONALE: Drugs used in chemotherapy work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Giving more than one drug (combination chemotherapy) may kill more tumor cells. Radiation therapy uses high-energy x-rays to kill tumor cells. It is not yet known whether giving methotrexate together with combination chemotherapy and radiation therapy is more effective than combination chemotherapy and radiation therapy alone in treating gliomas.