Oxaliplatin, Gemcitabine, Erlotinib, and Radiation Therapy in Treating Patients With Unresectable and/or Metastatic Pancreatic Cancer or Biliary Tract Cancer

RATIONALE: Drugs used in chemotherapy, such as oxaliplatin and gemcitabine, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Erlotinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Radiation therapy uses high-energy x-rays to kill tumor cells. Giving oxaliplatin together with gemcitabine, erlotinib, and radiation therapy may kill more tumor cells. PURPOSE: This phase I trial is studying the side effects and best dose of oxaliplatin, gemcitabine, and erlotinib when given together with radiation therapy in treating patients with unresectable and/or metastatic pancreatic cancer or biliary tract cancer.