Pemetrexed, Gemcitabine, and Radiation Therapy in Treating Patients With Locally Advanced Pancreatic Cancer

RATIONALE: Pemetrexed may stop the growth of tumor cells by blocking some of the enzymes needed for their growth. Drugs used in chemotherapy, such as gemcitabine, 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. PURPOSE: This phase I trial is studying the side effects and best dose of pemetrexed when given together with radiation therapy in treating patients with locally advanced pancreatic cancer.