 RATIONALE: Drugs used in chemotherapy, such as gemcitabine and capecitabine, 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. It is not yet known which regimen of chemotherapy with or without erlotinib andor radiation therapy is most effective in treating pancreatic cancer. 