Gemcitabine in Combination With Either Cisplatin or Carboplatin in Treating Patients With Stage III or Stage IV Non-Small Cell Lung Cancer

RATIONALE: Drugs used in chemotherapy, such as gemcitabine, cisplatin, and carboplatin, 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. It is not yet known whether giving gemcitabine together with cisplatin is more effective than giving gemcitabine together with carboplatin in treating non-small cell lung cancer. PURPOSE: This randomized phase III trial is studying gemcitabine and cisplatin to see how well they work compared to gemcitabine and carboplatin in treating patients with stage III or stage IV non-small cell lung cancer.