The two Vietnamese reporters swapped their office clothes for the soiled shirts and shorts of poultry traders and loitered around the livestock market until their disguises soaked up the odor. Then, they recounted, each poked a hole in his shirt near the waist, hiding a tiny video camera barely an inch wide.

The men, Duc Trung and Hoai Nam, were posing as novice chicken sellers for an undercover report at a slaughterhouse in Ho Chi Minh City. They used their cameras to document pre-dawn activities in which merchants purchased fake health certificates that claimed their birds were free of avian influenza, the journalists recounted. They also showed one poultry inspector asleep at his post.

The report, published three months ago in the Thanh Nien newspaper, called into question the national strategy for controlling bird flu, a disease that has killed at least 40 people in Vietnam, more than in any other country.

Although the expose infuriated some local agriculture officials, it demonstrated that news organizations in Vietnam now have the ability to play a role in uncovering public wrongdoing.

Officials at the city veterinary agency at first challenged the reporters' findings, and the owner of the slaughterhouse demanded a meeting. "When he first came in, he was so upset and hostile," Duc Trung recounted. "We showed him our evidence."

After that, the local government took action. The People's Council, the city's top legislative body, praised the reporters, ordered officials to report back about the irregularities uncovered by the newspaper and called for reforms, the pair said. The veterinarian at the slaughterhouse they investigated was removed and procedures were tightened, they said.

A day after the story was published, the reporters said, they were tipped off by sources in the poultry market that two men speaking with northern Vietnamese accents had come "to find the authors and teach them a lesson." The reporters turned the information over to police.

While the investigative report was permitted by the communist government, analysts emphasized that the news media are blocked from addressing many sensitive political issues in Vietnam. They are unable to report about the workings of the Communist Party or investigate top officials, the analysts said. Television stations and newspapers, including Thanh Nien, remain state-controlled.

"They want it to be a little more free, but not totally free. They don't want it to get out of their control," an analyst said.

But as government reformers increasingly air their frustrations over widespread corruption, they have encouraged a new generation of journalists to ferret out graft. The reporting has focused on crooked traffic cops, on referees fixing soccer matches and on popular anger about poor public services.

The line is not always clear. When a journalist revealed a Health Ministry document about efforts to combat SARS two years ago, she was prosecuted for publishing a state secret. But a court found in her favor on the grounds that the document was eventually going to be made public, the analyst recalled.

Such journalism has contributed to the arrest of several officials, according to reporters. At times, it has also prompted the government to revamp programs, such as the bird flu strategy, the Thanh Nien journalists said.

Duc Trung, 34, a university journalism graduate, has worked at the Thanh Nien newspaper for five years and said he had been attracted by its reputation for investigative reporting. Hoai Nam is 33 but he looks older. He never attended college but spent five years in the army and retired as a sergeant major.

"This guy looks like a chicken trader," Duc Trung said, patting his partner on the back during an interview at their newspaper's offices. "I don't look the part, but he does. That's why he was chosen for the project."

Their editors decided to tackle bird flu after the government announced it would launch a new drive against the virus in August, the reporters said. Dozens had already died in Vietnam from the virus, and tens of millions of chickens had died or been slaughtered in a bid to contain the epidemic since it was reported nearly two years ago. But the reporters heard from sources that efforts to ensure that only healthy poultry entered the country's largest city, Ho Chi Minh City, were a sham.

Duc Trung and Hoai Nam said they received coaching on how to behave, what to wear and what to say before going underground. They decided everything would be documented on videotape. While many U.S. newspapers, including The Washington Post, do not allow their reporters to work undercover, the reporters said it was essential to their project.

Shortly before 4 a.m. one August night, in a teeming quarter of the city, they approached the Manh Thang slaughterhouse, cited months earlier by the city for health violations. Barefoot, like other retailers, they entered the building. It was chaos, they recalled, a cacophony of bantering traders, screeching chickens and a roaring plucking machine.

On a table, they spotted two baskets stacked with purported health certificates called quarantine papers that had been stamped and signed. A staff veterinarian told the reporters they could buy one for 20 cents. It would allow them to claim that their own birds were free of disease, and it could be used over and over.

The pair returned to the slaughterhouse on four more nights. Each time, the reporters obtained certificates without buying any chickens, they recounted.

Over the course of a week, Duc Trung and Hoai Nam also monitored three of the city's main inspection stations, modest sheds erected along the highways entering the city. This time the reporters used a handheld video camera largely concealed in a plastic bag.

The inspectors were required to check that truckers hauling live animals had health certificates for all their livestock and that the number of animals roughly matched the figure given on the license. But the officials took only a cursory look at the paperwork and never inspected the trucks, the reporters found. At the post on the Hanoi highway, the reporters said they discovered an official asleep behind the station.

After a month of research and 10 days of undercover reporting, the team published its findings under the headline: "Quarantine Papers are Sold Like Vegetables!"

"Facing the risk that bird flu might break out, the authorities of this crowded city should have the feeling they were sitting on fire," the article concluded. "But according to how the work of inspections is carried out, the prospect of bird flu breaking out is unavoidable."

The Thanh Nien report was the most detailed of several recent Vietnamese media accounts about flaws in government programs to ban live poultry from urban areas and vaccinate birds against the virus.

Besides highlighting bribery at the slaughterhouse, Duc Trung and Hoai Nam documented the failure of government officers at three of Ho Chi Minh City's main roadside inspection stations to regulate the transport of poultry into the city from neighboring provinces, where the highly lethal virus is widespread in birds. In one instance, the reporters wrote, the officer in charge was asleep on the job.

"It was risky for us. The people at the market and the people at the slaughterhouse would threaten us if they knew what we were doing," Duc Trung admitted. "And we were exposed to all those chickens and their virus. They were supposed to be vaccinated, but God knows if they really were."

Despite difficulties and potential dangers, the reporters said they were ready to resume digging into the bird flu program if their sources notified them of more corruption in the containment efforts.

"If we were afraid, we'd never become investigative reporters," Duc Trung said. "We know we'll be threatened when we start an investigation, and we're ready to face the threats."

An Lac inspection station on the highway into Ho Chi Minh City was erected to inspect trucks carrying livestock. Thanh Nien's reporters monitored three sites and found that inspectors barely checked paperwork against truckloads.Hoai Nam, left, and Duc Trung in the newsroom of Thanh Nien. The pair posed as chicken sellers and found fake health bills on sale in Ho Chi Minh City.