OBJECTIVES: I. Determine the maximum tolerated dose of gemcitabine and cisplatin that can be administered during a standard course of radiation therapy for patients with unresectable or locally recurrent pancreatic and gastric cancer. II. Describe the tolerance of gemcitabine, cisplatin, and radiation therapy in this patient population. III. Seek preliminary evidence of the therapeutic activity of this regimen in this patient population as measured by survival.