But analysts warn that until the leadership is willing to introduce political changes that would allow real supervision of growth-hungry bureaucrats, the new emphasis on green growth will do little more than slow environmental devastation.

"They are seriously interested because they recognise that it impinges on a range of other issues that are important to them," said Elizabeth Economy, author of "The River Runs Black", a book cataloguing China's environmental challenges. "The question is do we get a leader in China who seizes the issue and realises that to clean up he or she needs to open up the system."

The engineers who rule China now were brought up on Chairman Mao Zedong's declaration that "man must conquer nature" for the sake of economic progress.

But to officials whose claim to legitimacy rests on growth and stability, the costs of this battle have become clear enough to force a change of direction.

Air quality in some Chinese cities is among the most polluted on the planet, causing hundreds of thousands of premature deaths each year. Its water is so contaminated that in some areas it is unsafe even to touch, let alone use for irrigation or drinking.

Already the world's top emitter of sulphur dioxide, which causes acid rain, China looks set to overtake the United States as the biggest producer of greenhouse gas carbon dioxide this year or next. Smog from its factories clouds skies in neighbouring countries.

"The environment will come up as a major issue at the 17th Party congress because China's pollution problem has become a global issue", said Yang Jing, of the University of Auckland.

"So to improve its image, it is important to make some kind of statement, or be seen to be making some kind of statement."

NEW LEADERS, NEW LANGUAGE

Some of China's new leaders have risen on the back of a growing awareness of the challenges of pollution, although few if any are personally committed environmentalists, analysts say.

Commerce Minister Bo Xilai, mooted as a possible vice premier, won kudos for his green revamping of the northeastern port of Dalian. Premier Wen Jiabao also appears to have thrown his weight behind new environmental priorities, with a solid grasp of technical, political and economic obstacles to change.

And when the Party opens its five-yearly congress on Monday, it is expected to write into its charter the theory of "scientific development" propounded by Party chief and state president Hu Jintao.

Arcane as the phrase may sound, it represents a landmark change of mentality to deal with troubles, from pollution to a yawning rich-poor gap, spawned by the get-rich-quick ethos of predecessor Jiang Zemin's era.

"So much in the Communist Party has to be legitimised in language, because it's a very strong signal of intention and direction, it's a major means of communication down to people at the village level," said Leo Horn, national coordinator of the UK-China sustainable development dialogue.

LOCAL RESISTANCE

But whether local officials choose to listen to the message, and how Beijing can enforce it in provinces with considerable autonomy, casts a shadow over the drive for a greener economy.

The leadership says performance on energy and environmental goals will be key to officials' career prospects.

But a project to factor the environmental cost of growth into state data was recently suspended, suggesting that even at a time of double-digit expansion officials are still in two minds about sacrificing growth for greener development.