BANGKOK » In southern China, the worst drought in at least 50 years has dried up farmers' fields and left tens of millions of people short of water.

But the drought has also created a major public relations problem for the Chinese government in neighboring countries, where in recent years China has tried to project an image of benevolence and brotherhood.

Farmers and fishermen in countries that share the Mekong River with China, especially Thailand, have lashed out at China over four dams that span the Chinese portion of the 3,000-mile river, despite what appears to be firm scientific evidence that low rainfall is responsible for the plunging levels of the river, not China's hydroelectric power stations.

This weekend, four affected countries—Myanmar, Laos, Cambodia and Vietnam—are meeting in Thailand to discuss the drought, among other issues.

Thailand will be requesting “;more information, more cooperation and more coordination”; from China, said Panitan Wattanayagorn, a government spokesman.

China has begun a campaign to try to counter the perception that its dams are hijacking the Mekong's water as the river runs from the Tibetan Plateau to the South China Sea.

Chinese officials, normally media shy, recently held a news conference and have appeared at seminars, including one on Thursday, to make their case that the drought is purely a natural phenomenon.

“;More information will help reduce misinformation,”; said Yao Wen, the head of the political section at the Chinese Embassy in Bangkok.

He presented pictures of sun-baked riverbeds and dried-up wells at the seminar, including one of a man straddling cracks in a dry riverbed.

“;This old man used to be a boatman, but now he has nothing to do,”; Yao told participants.

The concluding image was that of a child staring longingly into a bucket. “;You can see how serious the drought is,”; he said. “;It is a very, very terrible situation.”;

Still, many in the room continued to focus on China's dams. Yao listened to impassioned pleas by residents of northern Thailand to stop further construction on the river.

“;It's where we fish, where we get food,”; said Pianporn Deetes, a Thai campaigner for the environmental group International Rivers. “;It's where we feed our families.”;

She blamed Chinese dams and the blasting of rapids to make the river more navigable for reduced fish catches, and she criticized plans for more dams without more transparent public consultations.

By one recent count, there are more than 80 hydropower projects in various stages of preparation and construction for the Mekong and its tributaries.

“;How can you decide without listening to us?”; asked Pianporn, a native of Chiang Rai Province, in northern Thailand.

As in so many other parts of the world, the politics of sharing water are rife with tension. Within Thailand, where the drought has affected at least 14,000 villages, one official has described “;water wars”; between farmers hoping to keep their crops alive.

But discussions among the countries that share the Mekong are more complicated. A common approach toward planning the river's future means accommodating Thailand's lively and freewheeling society, the military dictatorship in Myanmar, the authoritarian democracy in Cambodia and the communist-ruled systems of Laos and Vietnam.

Many Thais remain particularly suspicious of Chinese plans for the Mekong, called Lancang in Chinese.

One professor at the seminar on Thursday prefaced a question to Yao, the Chinese diplomat, with this: “;I realize that it's difficult for you to speak freely—after this conference you would be fired if you talked freely.”;

Some conservationists have attributed the low river levels partly to the construction of China's fourth dam on the Mekong, at Xiaowan. The dam began filling its reservoir in July, during the rainy season, Chinese officials say, a process that was stopped with the arrival of the dry season.

In recent weeks, as water shortages became acute and navigation at some points of the Mekong became impossible, China released water from its dams, raising the water level, according to Jeremy Bird, the chief executive officer of the Mekong River Commission, an advisory body set up in 1995 by the governments of Cambodia, Laos, Thailand and Vietnam. China and Myanmar are not members but have some agreements to share information.

Overall, Bird says China has a “;limited capacity”; to reverse the effects of the drought for countries downstream. The Mekong, he says, has always been volatile.

“;Intense droughts and intense floods have been experienced for a long time,”; he said.

Bird and other experts say dams on the lower part of the river, including one planned in Laos, could have a harmful effect on migratory fish, among other problems.

But over all, Bird said he believed that more dams in China could even out the Mekong's seasonal variations by storing water when it was plentiful and releasing it when scarce.

For Pianporn, who says she cherishes the river's natural beauty and its bountiful fish, that argument is not persuasive.

“;We don't need more water in the dry season, and we don't need less in the wet season,”; she said. “;We would like to see the water as it is.”;