Gemcitabine With/Out Erlotinib in Unresectable Locally Advanced/Metastatic Pancreatic Cancer

DISEASE CHARACTERISTICS: * Histologically or cytologically confirmed adenocarcinoma of the pancreas * Locally advanced or metastatic disease that is considered unresectable * No known CNS metastases PATIENT CHARACTERISTICS: Age: * 18 and over Performance status: * ECOG 0-2 Life expectancy: * Not specified Hematopoietic: * Absolute granulocyte count at least 1,500/mm\^3 * Platelet count at least 100,000/mm\^3 Hepatic: * Bilirubin less than 2 times upper limit of normal (ULN) * AST and/or ALT less than 2 times ULN (5 times ULN if liver metastases present) Renal: * Creatinine less than 1.5 times ULN Cardiovascular: * No uncontrolled high blood pressure * No unstable angina * No congestive heart failure * No myocardial infarction within the past year * No cardiac ventricular arrhythmias requiring medication Gastrointestinal: * No gastrointestinal (GI) tract disease resulting in an inability to take oral medication such as uncontrolled inflammatory GI disease (e.g., Crohn's disease or ulcerative colitis) * No post-surgical malabsorption characterized by: * Uncontrolled diarrhea that results in weight loss and vitamin deficiency OR * Requires IV hyperalimentation * Pancreatic enzyme supplementation allowed provided that the above criteria are not met Ophthalmic: * No ocular inflammation or infection unless fully treated prior to study * No significant ophthalmologic abnormalities, including the following: * Severe dry eye syndrome * Sjogren's syndrome * Keratoconjunctivitis sicca * Severe exposure keratopathy * Disorders that would increase the risk for epithelium-related complications (e.g., bullous keratopathy, aniridia, severe chemical burns, or neutrophilic keratitis) Other: * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * HIV negative * No serious active infection * No other serious underlying medical, psychological, or geographical condition that would preclude study participation * No prior allergic reaction to compounds with similar chemical or biologic composition to erlotinib * No other prior malignancy within the past 5 years except cancer in situ or basal cell or squamous cell skin cancer PRIOR CONCURRENT THERAPY: Biologic therapy: * No concurrent biologic therapy or immunotherapy Chemotherapy: * No prior chemotherapy except fluorouracil (with or without leucovorin calcium) or gemcitabine administered concurrently with radiotherapy as a radiosensitizer * No other concurrent cytotoxic chemotherapy Endocrine therapy: * Not specified Radiotherapy: * See Chemotherapy * At least 4 weeks since prior radiotherapy and recovered * Prior radiotherapy for local disease allowed if evidence of disease progression has occurred * No concurrent radiotherapy Surgery: * See Disease Characteristics * At least 2 weeks since prior major surgery * No concurrent ophthalmic surgery Other: * No prior epidermal growth factor receptor inhibitors * At least 2 weeks since prior investigational drug * No other concurrent investigational drugs during and for at least 30 days after study * No other concurrent anti-cancer therapy