BEIJING -- One month ago, China was staging the closing ceremony of the Olympiad, basking in a haul of gold medals and praise for nearly perfect management of the summer games.

Today, it is struggling with another crisis in a year that, aside from those two weeks in August, has been filled with scandal, natural disasters and ethnic troubles.

The revelation that adulterated infant formula has killed at least four Chinese children and sickened 50,000 has presented rulers with a serious quality-control issue as well as a daunting political challenge. Officials face suspicions that they knew about the crisis months ago but did not disclose it in order to avoid dampening the Olympic party.

This crisis has hit particularly hard, in part because the impact is so widespread. The contaminated brands are nationally known and supposedly China's best. The news comes after similar scandals and a campaign to improve the quality control of Chinese products. And, while any parent would be angry, it also affects the generation of China's one-child policy.

Particularly disconcerting for many is evidence that so many producers were involved while regulators stood by, that warnings were ignored and that knowledge of the tampering appeared to be widespread. What started earlier this month as news that Sanlu Group Co. was selling milk powder containing the industrial chemical melamine ballooned within days to include 22 companies.

Tang Zhongjun, father of 18-month-old Fukun, said his family used Sanlu milk products since their son's birth because of their reputation. Several of the involved companies had been considered so safe that they were not subject to inspections.

But four months ago, Fukun started throwing up, suffering from diarrhea and having trouble urinating. His parents took him to four hospitals and eventually discovered that he had three large kidney stones.

Mr. Tang says he doesn't plan to sue as long as the government compensates the family adequately.

Melamine also was at the heart of a scandal last year in which North American pets died after eating Chinese-made pet food. It was reportedly added by suppliers to make products appear protein rich. Ingesting the chemical, used in plastics and fertilizer production, risks malnutrition and destroyed kidneys.

Previous quality-control scandals have involved Chinese-made toothpaste, seafood, tires, medicine and toys. Analysts say they underscore the downside of a political system in which accountability is limited and conflicts of interest rife.

"The Chinese Communist Party might be able to calm things down this time," said Alfred Chan, a professor with Canada's University of Western Ontario. "The danger is that things accumulate to an eventual breaking point. This is an emotional issue that greatly affects the population, one that has received a great deal of publicity and shows the party in a very unflattering light."

The Internet has been ablaze with comments.

"Where are the concerned parties that are supposed to inspect the quality?" asked user myy8206 on the discussion forum xici.net. "They should be taken out and shot!"

The milk scandal is the latest headache for leaders who have grappled with a February storm, riots in Tibet in March, the protest-marred Olympic torch relay in April and a massive earthquake in Sichuan in May. It highlights the cozy relationship between money and power in China. Sanlu's chairwoman, since fired, was an important local Communist Party official.

"The reality in China is there's no separation at all," said Arthur Kroeber, Beijing-based editor of China Economic Quarterly. "Its endemic."

As the scandal has intensified, the Communist Party has fallen back on traditional damage-control tactics. It has arrested 19 people and removed several officials, including the longtime head of the main government watchdog agency. It has restricted news about the scandal in the mainstream media. And it has warned lawyers trying to represent the victims.

"We've been told not to talk to the foreign press," said one attorney trying to help victims obtain compensation.

Many of the same tactics were used to quell parental anger at shoddy school construction after a disproportionate number of students died in the Sichuan earthquake in May. But with each major crisis, some analysts said, it becomes more difficult to contain the anger below the surface.