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BEIJING, Aug 7 (Reuters) - China's drive to improve energy efficiency lost pace in the first half of 2008, data showed on Thursday, as the world's top carbon dioxide emitter struggles to rein in wasteful energy use without upsetting the economy.

The country used 2.88 percent less energy to generate each dollar of national income in the six months to June than the same period the previous year, the National Bureau of Statistics (NBS) said. Last year it had cut its energy intensity by 3.66 percent.

China wants to cut pollution and decrease its dependence on imported fuels, but its double-digit economic growth and use of coal for four-fifths of its power generation have pushed it ahead of the United States as the top producer of CO2.

China set a target of improving energy intensity by 4 percent a year from 2006, but ultimately managed only a 1.79 percent improvement that year. Since then it has dropped the explicit 4 percent annual goal, saying only that it would stick to its overall target of a 20 percent cut by the end of the decade.

The NBS data showed some bright spots, with energy intensity in the construction materials industry dropping 9.98 percent in the first-half from a year earlier, the sharpest decline among major sectors.

Dai Yande, deputy head of Energy Research Institute, a government energy think-tank, said Beijing's clampdown on inefficient, energy-guzzling plants such as small cement makers have worked.

"Some sectors had previously expanded in a rough manner. Efforts to shut down small, inefficient plants in favour of big-scale ones have yielded results," Dai, a long-time researcher on energy saving, told Reuters.

A steep 9.61 percent decline in the textile industry reflected the closure of many small, export-focused textile manufacturers as they couldn't compete with bigger peers, he said.

But intensity in the petroleum and petrochmeical sectors showed just a 1.58 percent cut.

The NBS did not provide any further details or commentary on the numbers.

Beijing has tightened loans for polluters, accelerated closures of small coal mines and power stations and made energy efficiency a performance yardstick for provincial officials seeking promotion. (Reporting by Jim Bai and Chen Aizhu; Editing by Michael Urquhart)

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