DISEASE CHARACTERISTICS: Histologically or cytologically confirmed recurrent, locally advanced, or metastatic, unresectable non-small cell lung cancer Failed or relapsed after one prior platinum containing regimen (cisplatin or carboplatin) as first line therapy Prior brain metastases allowed if resection and/or radiotherapy completed, no worsening of CNS symptoms, and at least 1 month since prior corticosteroids

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: Karnofsky 70-100% Life expectancy: Greater than 12 weeks Hematopoietic: Absolute neutrophil count at least 2,000/mm3 Platelet count at least 100,000/mm3 Hepatic: Bilirubin no greater than 1.5 times upper limit of normal (ULN) AST or

ALT no greater than 3 times ULN (no greater than 5 times ULN in patients with liver metastases) Renal: Creatinine clearance at least 50 mL/min Other:

Able to swallow intact study capsules No active infection No life threatening illness (other than tumor) No prior malignancy within the past 5 years except well controlled nonmelanomatous skin cancer Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics At least 4 weeks since prior chemotherapy No more than one prior regimen of chemotherapy No prior gemcitabine No prior CI-994 At least 4 weeks since prior maintenance or consolidation therapy (e.g., matrix metalloprotein inhibitors) Endocrine therapy: See Disease Characteristics Radiotherapy: See Disease Characteristics At least 4 weeks since prior radiotherapy to primary site Surgery: Not specified