PUNE/CHANDIGARH, India, Aug 14 (Reuters) - After two weeks of dry weather India's cotton crop, sown on 13 percent more acreage this year, needs good rains in the next seven days to head off pest attacks and output loss, officials and farmers said on Friday 14 August.

Cotton planting, which has been nearly completed in most regions, has expanded to 9.4 million hectares, including 3.5 million hectares in Maharashtra, the country's biggest cotton growing state.

But monsoon rains that have been 29 percent short of normal since the season began on June 1 to Aug. 12, and have been unevenly spread, threatening the crop.

"In the last 10-12 days there was no rain in key producing districts," Purushottam Raut, director at Maharashtra's agriculture department, told Reuters.

The area under cotton in the western Maharashtra state has risen to 3.46 million hectares from 3.13 million hectares a year ago.

"If the dry spell continues for next 7 days, conditions will become favourable for pest and disease infestations due to increased temperature and humidity. This may affect per hectare yield," Raut said.

He said the situation was not serious yet but there were reports of some pest attacks, which increase in hot and humid conditions created by sporadic summer showers.

Officials in neighbouring Gujarat state said the crop area would rise to 2.6 million hectares from 2.5 million already planted, compared with average planting of 2.35 million hectares in previous years.

State government officials said the crop can withstand dry weather for only one more week. After that, output may shrink 5-10 percent instead of the expected 4.5 percent rise.

While Maharashtra leads in terms of area, Gujarat tops it in productivity.

In northwestern and central India, the prolonged dry spell may reduce cotton output by 10-15 percent and cotton quality may also suffer, officials and traders said.

In July, output from Punjab, Haryana and Rajasthan was estimated to be about 4 million bales, said Rakesh Rathi, president of North India Cotton Association.

"It could be revised if there is no rain in the next seven days," he said.

From June 1 to Aug. 12, rainfall has been 35 percent below normal in Punjab and 56 percent short in Haryana, two leading agricultural states, said Chatar Singh, director of the Chandigarh office of the India Meteorological Department.

Gurdial Singh, joint director with the Punjab farm department, said the crop would gain if it rains in the next 10 days.

Area under cotton in Punjab, the fourth-biggest producer, has increased marginally to 530,000 hectares from 527,000 hectares in 2008/09. In Haryana, the area under the crop is 527,000 hectares.

In central Madhya Pradesh, the dry spell may hit cotton output by 10 percent, although the crop has been planted in 650,000 hectares, up from 625,000 hectares last year, a government official told Reuters.

India produced 23.2 million bales (1 bale = 170 kg) in 2008, the federal farm ministry data showed.

(By Ramesh Jadhav and Ikhhlaq Singh Aujla. Additional reporting by Ashish Tiwari in Bhopal, Vikas Vasudeva in Chandigarh, Darshan Mankad in Ahmedabad and Arvind Sharma in Jaipur; Editing by Ranjit Gangadharan)