Six years after major U.S. tobacco companies agreed to restrict cigarette advertising as part of a $246 billion settlement, “Big Tobacco” is fighting for survival. U.S. sales have plummeted in the past three years, tobacco taxes have risen, and smoking has been banned in airplanes, buses and restaurants. Nonetheless, a quarter of American teens are smokers by the time they leave high school, tobacco exports to Asia are booming, and lawmakers recently defeated a bill authorizing the Food and Drug Administration to regulate tobacco products. But tobacco use is still the leading preventable cause of death in the United States, and industry critics complain that cigarette ads and controversial, new products — including flavored cigarettes — target minors. The industry's prospects may well rest on the outcome of two suits by smokers and a $280 billion Justice Department action charging cigarette makers conspired to defraud the public about the risks of smoking.