Triacetyluridine and Fluorouracil Compared With Gemcitabine in Treating Patients With Unresectable Locally Advanced, or Metastatic Pancreatic Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed adenocarcinoma of the pancreas * Unresectable locally advanced or metastatic disease * Stage II, III, or IV * Measurable or evaluable disease * No elevated tumor marker (CA 19-9) only * No clinically significant third-space fluid accumulation (e.g., ascites or pleural effusion) * No carcinoid, islet cell, or lymphoma of the pancreas * No prior or concurrent brain or leptomeningeal metastases PATIENT CHARACTERISTICS: Age: * 18 and over Performance status: * Karnofsky 70-100% Life expectancy: * At least 3 months Hematopoietic: * WBC at least 3,500/mm\^3 * Platelet count at least 100,000/mm\^3 * Hemoglobin at least 9.5 g/dL Hepatic: * Bilirubin no greater than 2.0 mg/dL * ALT or AST less than 3 times upper limit of normal (ULN) (5 times ULN if liver metastases present) * No uncontrolled hepatic dysfunction Renal: * Creatinine less than 2.0 mg/dL * No uncontrolled renal dysfunction Cardiovascular: * No uncontrolled cardiovascular disease requiring therapy, including the following: * Angina * Arrhythmias * Uncompensated cardiac failure * Myocardial infarction within the past 6 months Pulmonary: * No uncontrolled pulmonary dysfunction Gastrointestinal: * Able to take and/or retain oral medication * No uncontrolled malabsorption syndrome or any other condition that would interfere with intestinal absorption Other: * No known allergy to fluorouracil (5-FU), gemcitabine, triacetyluridine, or any of their components * No dihydropyrimidine-dehydrogenase deficiency * No active uncontrolled infection * No uncontrolled neurologic or psychiatric dysfunction * No other malignancy except previously resected basal cell cancer or curatively resected stage I or less cervical cancer that has been disease free for at least 5 years * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * HIV negative PRIOR CONCURRENT THERAPY: Biologic therapy: * No concurrent biologic therapy (including immunotherapy) for cancer Chemotherapy: * No prior chemotherapy for cancer other than as a radiosensitizer * No prior 5-FU or gemcitabine other than as a radiosensitizer * No prior triacetyluridine * No other concurrent chemotherapy (including leucovorin calcium) for cancer Endocrine therapy: * No concurrent hormonal therapy for cancer * Concurrent megestrol, oral contraceptives, or postmenopausal estrogen replacement therapy allowed Radiotherapy: * Prior radiotherapy allowed * No concurrent radiotherapy Surgery: * See Disease Characteristics * Prior resection of pancreas allowed Other: * At least 30 days since prior investigational drug or therapeutic device * No other concurrent anticancer therapy * No other concurrent investigational drugs or devices * No concurrent drugs that would interact adversely with 5-FU or gemcitabine