The government has been struggling to deal with festering health and public-relations issues since the crisis erupted last month. China's food exports have increasingly suffered, with more nations issuing import bans.

The melamine contamination has been blamed in the deaths of four babies and for sickening more than 54,000 children. Melamine, used in such products as plastics, paint and adhesives, can lead to kidney stones and possibly life-threatening kidney failure.

Dairy suppliers have been accused of adding melamine to watered-down milk to make the product appear rich in protein and to fool quality-control tests. There had been no previous standards.

Under guidelines adopted yesterday, melamine limits considered safe are set at one part per million for infant formula and 2.5 parts per million for liquid milk, milk powder, and food products that contain more than 15 percent milk.

Any items containing higher levels will be "prohibited from sale," said Wang Xuening, a Health Ministry official.

Wang acknowledged that small amounts of melamine could leach from the environment and packaging into milk and other foods, but said that deliberate tainting was explicitly forbidden.

Chen Junshi, a researcher for China's Center for Disease Control and Prevention, said the new guidelines would help officials assess whether melamine had been intentionally added or existed in the environment.

Levels of melamine found in batches of milk powder recently registered as much as 6,196 parts per million.

In the United States, the Food and Drug Administration says its experts have concluded that eating 2.5 parts per million of melamine - a minuscule amount - would not raise health risks, even if a person ate food every day that was laced with it.

China's cabinet has acknowledged that the country's dairy industry was "chaotic" and suffered from a grave lack of oversight. It has pledged to monitor milk products from dairies to store shelves.