DISEASE CHARACTERISTICS: Histologically confirmed unresectable or metastatic biliary tract carcinoma (extrahepatic, intrahepatic, or ampulla of Vater) or gallbladder carcinoma Not amenable to combined chemotherapy and radiotherapy CNS metastases that are locally treatable (i.e., lesions treatable with surgery or radiotherapy) allowed if no evidence of progression for at least 4 weeks after completion of treatment

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: Not specified Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 3.0 times upper limit of normal (ULN) AST no greater than 5 times ULN Renal: Creatinine no greater than 1.5 times ULN Other: Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception No other malignancy within the past 5 years except basal cell or squamous cell skin cancer or carcinoma in situ of the cervix

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior biologic or immunologic therapy No prior biologic or immunologic therapy for metastatic disease No concurrent immunotherapy No colony stimulating factors administered concurrently with first course of study therapy, or within 24 hours prior to subsequent courses Chemotherapy: See Disease Characteristics No prior gemcitabine No prior chemotherapy for metastatic disease At least 6 months since prior chemotherapy used as radiosensitization either in the adjuvant setting or for locally advanced disease No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics No prior radiotherapy to more than 25% of bone marrow No concurrent radiotherapy Surgery: See Disease Characteristics