RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Combining chemotherapy with radiation therapy may kill more tumor cells.

PURPOSE: Phase II trial to study the effectiveness of gemcitabine plus radiation therapy in treating patients with pancreatic cancer that cannot be removed surgically.

OBJECTIVES: I. Estimate time to progression and overall survival of patients with locoregional adenocarcinoma of the pancreas treated with gemcitabine combined with radiation therapy. II. Estimate the biomarker response to this regimen through evaluation of circulating CA19-9 levels and correlate this response with survival of this patient population.

OUTLINE: Patients receive radiation therapy 5 days per week for 5 1/2 weeks and gemcitabine IV over 30 minutes not greater than 2 hours prior to radiation therapy twice weekly. This combination radiation therapy and chemotherapy is followed by 2 weeks of rest. Patients with stable or responding disease receive a higher dose of gemcitabine IV over 30 minutes weekly for 3 weeks followed by 1 week of rest. This 4 week course is repeated 3 more times for a total of 16 weeks of gemcitabine therapy alone. Patients are followed every 2 months for the first year and then every 3 months for the next 2 years or until disease progression. Upon documentation of disease progression, patients are followed every 3 months for survival and secondary malignancy.

PROJECTED ACCRUAL: A total of 40 patients will be accrued for this study within 24 months.

DISEASE CHARACTERISTICS: Histologically confirmed adenocarcinoma of the pancreas Locoregional and not amenable to surgery based on 1 or more of the following: Size of pancreatic tumor greater than 5 cm Lymph nodes bulky, greater than 2 cm, but within radiation port Vascular involvement or impingement of major vessels (e.g., superior mesenteric artery, superior mesenteric vein, portal vein, hepatic artery) Involvement of colon (head lesions) or involvement of adrenal, kidney, or colon (tail lesions) Patients must be registered and begin treatment within 42 days of surgical staging No metastatic disease or nodal disease outside of radiation port documented by CT scan or MRI and chest x-ray

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: Not specified Hematopoietic: Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Albumin greater than 3 g/dL Bilirubin less than 2.0 mg/dL Renal: Creatinine less than 2.0 mg/dL Calcium normal Other: No prior or concurrent malignancy within the past 5 years except inactive nonmelanoma skin cancer, carcinoma in situ of the cervix, or other curatively treated cancers Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior biologic therapy for carcinoma of the pancreas Chemotherapy: No prior chemotherapy for carcinoma of the pancreas No other concurrent chemotherapy Endocrine therapy: No prior endocrine therapy for carcinoma of the pancreas No concurrent hormone therapy (except for nondisease-related conditions) Radiotherapy: No prior radiation therapy for carcinoma of the pancreas No prior abdominal radiation therapy Surgery: See Disease Characteristics No prior surgery for carcinoma of the pancreas