RATIONALE: Gefitinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Drugs used in chemotherapy, such as gemcitabine and cisplatin, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Giving more than one drug (combination chemotherapy) may kill more tumor cells. Giving gefitinib as first-line therapy followed by gemcitabine and cisplatin after disease progression may be an effective treatment for non-small cell lung cancer.