BEIJING, April 18 -- China's Communist leaders today declared a nationwide war on the SARS virus and ordered officials to stop covering up the extent of the epidemic that is spreading throughout China.

Following an extraordinary session of the Politburo on Thursday, the front page of every Chinese newspaper today reported an order by President Hu Jintao that all party organs and government agencies launch a campaign against the disease, "relying on science, effective prevention, and increased coordination."

Hu warned that SARS would affect the course of China's "development and stability," and acknowledged unspecified "existing problems" in dealing with the epidemic. "The meeting explicitly warned against the covering up of SARS cases and demanded the accurate, timely and honest reporting of the SARS situation," the New China News Agency said.

The extraordinary nature of the campaign was reiterated on the nightly TV news in a report about Premier Wen Jiabao. The reports heralded the start of a nationwide campaign against the disease -- the Communist Party's traditional way of dealing with crises, floods, unruly religious sects and other challenges to the government.

World Health Organization officials say they expect China will soon substantially increase its tally of infected people here, already the highest in the world. At least 3,461 people have been infected by the SARS virus worldwide and at least 170 people have died, according to WHO statistics. Most of the cases have been in China and Hong Kong.

China's government has been widely criticized here and abroad for responding slowly to the threat of severe acute respiratory syndrome, or SARS, which is believed to have erupted in Guangdong province in southern China in November. Officials have been blamed for failing to report the disease to other provinces and other countries.

Authorities in Beijing are suspected of having significantly underreported the number of SARS cases in the capital. On Wednesday, WHO said there were probably as many as 200 people in Beijing infected with SARS, although the city government insisted there were only 37 cases.

Health care workers said they were ordered to underreport cases in Beijing because city officials were afraid WHO would issue a travel advisory for the capital. Earlier this month, WHO issued an advisory against unnecessary travel to Hong Kong and Guangdong, the first such warning in its 55-year history.

Wen, the Chinese premier, visited a kindergarten, elementary school, high school and university in Beijing today to underscore concerns that SARS is present in schools. "A responsible government must at all times put the people's interests first," he said. "We will never allow slow reporting, failure to report or misreporting, otherwise we will seriously investigate the responsibility of the relevant official."

Wen's remarks brought speculation that a senior Chinese official might be fired for lying to the public. This would be an unprecedented move for a government that rarely, if ever, admits mistakes. Health Minister Zhang Wenkang, a former military doctor, is a possible target, having denied at an April 4 news conference that there were delays in cooperation with international researchers and that officials misreported health statistics.

James Maguire, who heads the WHO team researching SARS in China, said Zhang informed the team today that China has changed its rigid definition of what constitutes a probable SARS case. Maguire, an epidemiologist with the U.S. Centers for Disease Control and Prevention, said the number of cases listed in China would "significantly increase" as a result.

China's SARS epidemic is an early challenge to the two-month-old government led by Hu and Wen. Analysts, scientists and medical professionals are comparing the damage done to China's international reputation to the aftermath of the 1989 Tiananmen Square crackdown, when China crushed student-led protests.

Said one leading Chinese scientist: "When I went to France, my colleagues looked at me and said, 'We might be able to understand Tiananmen Square. That was your internal affair. But here your failure has cost lives around the world.' I could only agree."

Chinese health specialists are concerned that the government may be responding to the disease too late to control its spread across the country. At least eight of China's poorer provinces, including Shanxi, Inner Mongolia and Ningxia, have reported SARS cases. Officials said hospitals in those areas may not be able to cope with contagion and the influx of patients.

Guangdong, China's wealthiest province to the southeast, appears to have contained the rate of infection through stringent measures in hospitals and other facilities, according to WHO officials. They said Beijing, with its strong health care infrastructure, also may be able to control the spread of the disease.

"But we are worried about the interior," said Henk Bekedam, a WHO official. "They have fewer resources and less experience. They need lots of help."