TOKYO, May 7 (Reuters) - China said greenhouse gas curbs for heavy polluting industries like cement and steel are an important tool for fighting climate change, a concession that could bolster talks on a new global deal to control emissions.

But Beijing's support, unveiled in a joint statement on climate change made during Hu Jintao's first state visit to Japan as Chinese President, stopped short of a full endorsement of the the "sectoral approach" that Tokyo is promoting heavily.

"The Chinese side expressed a view that sectoral approaches in fighting climate change is an important method, and both sides will further study what role such approaches can serve," a summary of the joint statement released on Wednesday said.

A top Japanese business leader and steelmaker said in April that curbs on five key sectors -- power generation, steel, cement, electric appliances and automobiles -- would cover some 70 percent of global emissions.

But many developing countries are suspicious that the scheme might throttle their inefficient energy-intensive businesses while allowing rich nations responsible for the majority of past emissions to ease curbs on new ones.

Activists also warned that the details of how any set of sectoral curbs would work was still very much up for grabs -- and China remained suspicious despite its public show of support.

"China fears a sectoral approach will undermine the current commitments from developed countries, and is one way of getting developing countries to do what is not fair," said Yang Ailun, climate and energy campaign manager at Greenpeace in China.

"If you look closely about the definition of what sectoral approach means it varies widely from country to country....China has not said no to the sectoral approach in general but they have expressed strong concerns about the Japanese proposal." The statement was a compromise that acknowledged both sides' positions, Yang added.

But it also showed that China, which took an active role at key U.N.-led talks in Bali late last year, has a constructive approach to the next stage of talks, said Jennifer Morgan, a director at environmental pressure group E3G.

"It demonstrates that they're there to play ball," she said.

The world aims to finalize a new pact to cut emissions at a meeting in Copenhagen at the end of 2009, which would give signatories two years to ratify the deal before the 2012 expiry of current emissions targets set by the U.N.'s Kyoto Protocol.

CARBON MARKET BOOST?

Rich nations say a sectoral approach could provide a first step for developing countries to cut their contribution to climate change without sacrificing their economic growth.

The sectoral target could be set as a national or global benchmark -- possibly with different levels for developed and developing nations.

A global benchmark would have the extra benefit of reassuring industries in rich countries, worried that tougher climate change controls at home are creating competitive advantages for China, India and others.

Sectoral approaches could also scale up the global carbon market, providing much bigger sources of carbon offsets.

If China's steel industry, for example, became more efficient than its benchmark it could sell the difference as potentially lucrative emissions reductions on the swelling carbon market. (Additional reporting by Gerard Wynn in London, Writing by Emma Graham-Harrison; Editing by Sanjeev Miglani)

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