BEIJING -- A few weeks ago, Pang Jiaoming's career as a reporter ended, just two years after it began.

The Communist Party's Central Propaganda Department and the official All-China Journalists Association issued a directive ordering Pang's employer, the China Economic Times, not only to fire him, but also to "reinforce the Marxist ideological education of its journalists." In a separate notice to news organizations across China, Pang said, propaganda officials announced that he was also banned from further work as a reporter at other publications.

Pang's offense was a pair of articles reporting that substandard coal ash was being used in construction of a showcase railroad, the $12 billion high-speed line running 500 miles between Wuhan, in Hubei province, and Guangzhou, an industrial hub just north of Hong Kong. The ash is a key ingredient in concrete used for tunnels, bridges and roadbed, Pang wrote, and a substandard mix raised the specter of collapsing structures and tragic accidents.

Pang's report, which was published on the front page, illustrated the growing desire of young Chinese reporters to push the limits of the country's draconian censorship system. In a booming and fast-transforming economy riddled with corruption, they have found a fertile field for investigative journalism, along with readers increasingly hungry to know about malfeasance that affects their lives.

But his fate also dramatized how helpless China's journalists remain under the thumb of an authoritarian government that maintains a vast propaganda bureaucracy with unquestioned power to control what is published and decide who rises and falls in the news business.

Change has begun, with visible loosening since the 1970s. But the party's propaganda mandarins have retained the power to intervene whenever they decide to do so, and in the past several years they have intervened with increasing, although unpredictable, frequency. As a result, working as a reporter in China has come to mean succumbing as a compliant propagandist or dancing along the censors' red line -- making each story a high-stakes gamble on how far to go.

"China is a heaven for investigative reporting, since it has a lot of interesting things to cover, but it is not a heaven for Chinese investigative reporters," said Zhan Jiang, journalism dean at the China Youth University for Political Sciences in Beijing.

Pang, a slight Hainan Island native with a sparse mustache and hair hanging unfashionably down the back of his neck, had an unlikely background for someone trying to play the edge. He graduated in 2005 from the China Youth University for Political Sciences, which traditionally has been a training ground for the Communist Youth League once led by President Hu Jintao.

Nevertheless, Pang gravitated swiftly toward investigative journalism, focusing on economic corruption and environmental degradation.

Money wasn't the lure; Pang said he earned about $120 a month in salary and, with the per-word payments common in Chinese journalism, was able to add another $300. But Pang decided it was the work for him. Soon after starting, he wrote about pollution in Jiangsu province. Then he took aim at pollution in Shanxi province, coal mining corruption in Hunan province and abuse of pasture lands in Inner Mongolia. In his wake were dozens of local officials angered by the disclosures.

As a result, Pang became known at the Central Propaganda Department as someone willing to cross the line. His image was further defined by a sassy blog that featured drawings of the classic see-no-evil, hear-no-evil, speak-no-evil monkeys.

Pang's latest gamble began in June, when several letters arrived at his newspaper's Beijing headquarters. Because substandard ash was used in the mix, said a writer working on the railroad project, concrete was getting stuck in construction site funnels. After looking into the problems that substandard ash could cause and getting his editor's approval, Pang boarded a train south and launched his investigation. What he found, he said, were five factories selling ash rated below the national standard for use in concrete. Pang said he witnessed the substandard ash being loaded into trucks and mixed into concrete for use on the railroad. He had samples of the ash analyzed by two laboratories, which found it did not meet China's standards, he added.

There was a difference of about $12 a ton between the substandard ash, which contained rock and other waste, and the mandated fine ash, which comes mostly from the smoke of coal burned in power plants, Pang said. That meant a lot of money was being made from fraud, he suggested, probably at the railroad construction company as well as at the coal ash providers.

"If there was no cooperation between the railroad construction company and the sellers of the coal ash, how could all this be done?" he asked.

With its clear suggestion of corruption and safety hazards, the first article drew a swift reaction when it appeared July 4. Pang said his editors got calls from the Railway Ministry, the Central Propaganda Department and the All-China Journalists Association urging that nothing further be written on the subject.

The ministry and its Wuhan-Guangzhou Passenger Dedicated Line subsidiary issued denials, meanwhile, saying their own analyses showed that ingredients in the concrete met the standard. Undeterred, Pang published a second report July 24, offering further details from what he described as "inside sources" and repeating his allegations.

Angered by the challenge, and apparently responding to upset officials in the Railway Ministry, the Central Propaganda Department demanded to see Pang's documentation. Pang said he handed over his material as requested, but without revealing his sources. The next move by propaganda officials, he said, was to hold a meeting Aug. 27 between the newspaper editors, on one side, and on the other, railway officials, university specialists and a senior representative of the All-China Journalists Association. All of the latter condemned the stories, saying they had damaged the reputation of the railroad in China and abroad. A week later, an official ruling declared that the ash in question had been analyzed and was without problem. That was followed by the firing order.

"Our investigation showed that Pang's report was untrue and not comprehensive," said Sun Zhaohua, who attended the meeting as director of the self-discipline division at the All-China Journalists Association.

Pang said he was not surprised to see Sun join the attack on his stories. The journalists association does not represent journalists, he said, but serves as a wing of the Central Propaganda Department.

"I don't see anybody who protects us journalists," Pang said. "But maybe I can protect myself." To do so, he has continued his investigation, accumulating what he says is more scientific proof that substandard ash was used.

But aligned against Pang and his kind is a formidable propaganda bureaucracy that has been a key part of the Chinese Communist Party since the days of Mao Zedong.

Li Changchun, who guides the machinery as head of the Central Leading Group on Propaganda and Ideological Work, was just reappointed to the Politburo's Standing Committee, the apex of power in China. His deputy, Liu Yunshan, who was just reappointed to the Politburo, has since 2002 administered the Central Propaganda Department, headquartered in a new building next to the Zhongnanhai leadership compound and a few hundred yards from Tiananmen Square.

Liu's operation, with about 250 staff members, has been assigned mainly to monitor domestic information. Efforts to control, or at least influence, foreign information about China have been entrusted to the party's External Propaganda Leading Group, which merged 16 years ago with the State Council Information Office, according to David L. Shambaugh, a China specialist at George Washington University writing in the January issue of the China Journal.

In addition, the party's central bureaucracy has been replicated dozens of times in provincial and municipal offices around the country.

The New China News Agency, although an organ of the government, has been assigned a number of party propaganda officials to monitor reports from each department. The agency, ostensibly a public news purveyor, also has been tasked with writing internal government reports, providing the party and government with news the public is not allowed to see. A former editor said senior correspondents have long vied to write official reports rather than general news, hoping to get noticed by party cadres.

Pang said he was not dismayed by the odds despite his experience. His girlfriend, also from Hainan, has continued to work and bring in money, he said, adding, "Myself, I'll just have to wait and see for a while."