DISEASE CHARACTERISTICS: Histologically proven metastatic non-small cell lung cancer Eligible subtypes: Adenocarcinoma Squamous cell carcinoma Large cell carcinoma At least 1 bidimensionally measurable lesion, at least 2 cm by 2 cm in perpendicular diameter on radiologic study Previously irradiated bony lesions are not considered measurable unless there is evidence of disease progression at that site prior to study No brain metastases

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Life expectancy: More than 12 weeks Hematopoietic: Absolute neutrophil count at least 1,500/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9 g/dL Hepatic: Bilirubin no greater than 2 times upper limit of normal (ULN) SGOT and SGPT no greater than 2 times ULN (5 times ULN if documented liver metastases) Alkaline phosphatase no greater than 2 times ULN (5 times ULN if documented liver metastases) Renal: Blood urea nitrogen no greater than 1.5 times ULN Creatinine no greater than 1.5 times ULN Other: No active nonmalignant systemic disease that would increase risk No frequent vomiting or medical condition that would interfere with oral medication intake (e.g., partial bowel obstruction) No other malignancy within the past 5 years except surgically cured carcinoma in situ of the cervix or basal cell or squamous cell skin cancer HIV negative No AIDS-related illness Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent immunotherapy or biologic therapy No concurrent growth factors or epoetin alfa Chemotherapy:

At least 4 weeks since prior chemotherapy No more than 1 prior chemotherapy regimen for metastatic disease No other concurrent chemotherapy Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics Prior radiotherapy for local control or as palliative therapy for a painful bony lesion allowed No prior radiotherapy to 50% or more of bone marrow At least 4 weeks since prior radiotherapy to 15% or more of bone marrow (2 weeks for radiotherapy to less than 15% of bone marrow) and recovered No concurrent radiotherapy Surgery: Not specified Other: Recovered from any prior therapy No other concurrent investigational drugs