UN sets out massive benefits from air pollution action in Asia

* Air pollution health risk for 4 billion people in Asia

* Cleanup costs far outweighed by economic benefits - report

* Increasing political openness seen on taking action

GENEVA, Oct 30 (Reuters) - Asia could reap massive benefits in health, environment, agriculture and economic growth if governments implement 25 policies such as banning the burning of household waste and cutting industrial emissions, according to a U.N. report.

Air pollution is a health risk for 4 billion people in Asia, killing about 4 million of them annually, and efforts to tackle the problem are already on track to ensure air pollution is no worse in 2030, but huge advances could be made, the report said.

The report's 25 recommendations would cost an estimated $300 billion-$600 billion annually, a big investment but loose change compared with a projected $12 trillion economic growth increase.

The publication of the report, "Air Pollution in Asia and the Pacific: Science based solutions", on Tuesday coincides with the World Health Organization holding its first global air pollution conference in Geneva this week.

The recommendations also included post-combustion controls to cut emissions from power stations, higher standards for shipping fuels, ending routine flaring of gas from oil wells, and energy efficiency standards for industry and households.

The biggest gains would come from clean cooking, reducing emissions from industry, using renewable fuels for power generation and more efficient use of fertilisers.

Huge improvements in post-combustion controls and emission standards for road vehicles were already anticipated because of recent legislation, although both could be improved further.

Indeed, India may halt the use of private vehicles in the capital New Delhi if air pollution, which has reached severe levels in recent days, gets worse, a senior environmental official said on Tuesday.

Authorities in the capital have already advised residents to keep outdoor activity to a minimum from the beginning of next month until at least the end of the Hindu festival of Diwali on Nov. 7, when firecrackers typically further taint air choked by the burning of crop stubble in neighbouring states.

Helena Molin Valdés, head of Climate and Clean Air Coalition Secretariat at U.N. Environment, said there was increasing political openness to taking action on air pollution and the report reflected three years of discussions with governments.

"What the governments were saying in the region was: 'Dont tell us we have a problem, we know there is a problem, how can we deal with it and what will it take to do it?'," she said.

The report estimates its recommendations would cut carbon dioxide emissions by 20 percent compared to a baseline scenario, potentially decreasing global warming by one-third of a degree Celsius by 2050, which would also be a contribution in the fight against climate change.

One billion people would enjoy high air quality, while the number exposed to the worst pollution would be cut by 80 percent to 430 million. Premature deaths would fall by a third.

Crop yields would benefit because of a reduction in ozone, which is estimated to have cut 2015 harvests by 10 percent for maize, 4 percent for rice, 22 percent for soy and 9 percent across Asia, a total of 51 million tonnes. (Reporting by Tom Miles; Editing by Alison Williams)