This randomized phase III trial is studying temozolomide and radiation therapy to compare how well they work when given together with or without bevacizumab in treating patients with newly diagnosed glioblastoma. (gliosarcoma closed to accrual as of 07-13-10). Drugs used in chemotherapy, such as temozolomide, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to kill tumor cells. Monoclonal antibodies, such as bevacizumab, can block tumor growth in different ways. Some block the ability of tumor cells to grow and spread. Others find tumor cells and help kill them or carry tumor-killing substances to them. It is not yet known whether temozolomide and radiation therapy are more effective when given together with or without bevacizumab in treating glioblastoma or gliosarcoma