For 20 years, Chinese officials carefully measured this city's air pollution levels and equally carefully hid the results - fearing that the truth might tarnish the capital's image or lead to social unrest. This continued even as Beijing's famously blue sky turned ever more gray and its surrounding hills disappeared behind an acrid mist.

So it seemed a small miracle when, on Feb. 28, Beijing joined 38 other Chinese cities that have started to issue weekly air-quality reports in the last year.In newspapers and on television, they parade a sometimes eclectic mix of statistics - from levels of nitrous oxides produced by car exhausts to the concentration of tiny particles from coal burning in the air. And Chinese citizens for the first time have hard information on the air they breathe.

The data have confirmed what many Western scientists have suspected: that the air in China's cities is among the most polluted in the world. Recent research suggests that bad air in China causes 178,000 premature deaths each year.

The severity of the pollution, now openly acknowledged by the government, has propelled environmental issues onto the agenda of the Chinese-American summit meeting that is to take place later this month. Chinese officials say they are eager to have Washington's technical help in the battle for cleaner air.

But more than that, the government's candor has created a new political dynamic between the government and its people, feeding an environmental consciousness.

"The air is bad - you can read it in the newspapers," said Zhang Jiyan, from her roadside bathing-suit stand in downtown Beijing. "Look, you can't even see tall buildings a few streets from here."

"Releasing the numbers is a revolutionary concept for the people and the government," said Lu Xinyuan of the state Environmental Protection Agency. "We were worried that the people would complain that air pollution is too serious. Instead, the consciousness of people has been raised. And they feel the government trusts them with the facts, so we are gaining points by doing this."