Beijing's smog can choke first-time arrivals. Then there's the pervasive cigarette smoke, so much a part of China's culture that more than half of all male doctors smoke. That's about to change. Starting Thursday, the Chinese capital finally joins other major cities in cracking down on smoking in most public buildings. But even a communist government realized it could go only so far without stirring social unrest. Restaurants, bars and hotels can still allow smoking but must provide smoke-free areas or rooms. The smoking ban is the latest move toward the government's promise of a "smoke-free Olympics." To curb air pollution, a serious concern for athletes preparing for the Aug. 8-24 Games, Beijing decided to halt construction sites and half of road traffic. Now Beijing is tackling the health threat from secondhand smoke, which kills more than 100,000 Chinese nationwide every year, public health officials estimate. The anti-smoking drive dovetails with government efforts to improve citizens' behavior and present a modern image to the world for the Summer Games. Compared with government campaigns against spitting, littering and cutting into line, this initiative promises major health benefits. China has 320 million smokers, or 24.5% of the world's total, Sun Xianli, a senior city health official, said Thursday. The cost of lighting up The new regulation expands the current