Chinese military and security officials are forcing the elderly physician who exposed the government's coverup of the SARS epidemic to attend intense indoctrination classes and are interrogating him about a letter he wrote in February denouncing the 1989 Tiananmen Square massacre, according to sources familiar with the situation.

The officials have detained Jiang Yanyong, 72, a semi-retired surgeon in the People's Liberation Army, in a room under 24-hour supervision, and they have threatened to keep him until he "changes his thinking" and "raises his level of understanding" about the Tiananmen crackdown, said one of the sources, who described the classes as "brainwashing sessions."

But Jiang, who became a national hero last year after blowing the whistle on the government's efforts to hide the SARS outbreak, has refused to back down, and said in a recent note to his family that he would continue to "face the problems confronting me with the principle of seeking truth from facts," according to a person close to the family.

The standoff is the culmination of an extraordinary battle of wills that has been quietly unfolding for months between China's ruling Communist Party and an individual who has already challenged the authorities and forced them to back down once.

China's state-controlled media have not reported Jiang's detention, which began June 1. In response to questions submitted by The Washington Post, the government said in a brief statement: "Jiang Yanyong, as a soldier, recently violated the relevant discipline of the military. Based on relevant regulations, the military has been helping and educating him."

Though Chinese police routinely jail dissidents, the decision to detain Jiang appears to have been made by the Central Military Commission, the nation's supreme military body, with the consent of the party's most senior leaders, including President Hu Jintao and his influential predecessor, Jiang Zemin, according to a source familiar with the decision-making process.

The move represents a high-risk gamble by the leadership because of Jiang Yanyong's public stature at home and abroad. Photographs of his wizened face have been displayed on the covers of national magazines, and state newspapers have published articles crediting him with saving lives around the world by forcing government officials to confront the SARS epidemic.

If the leadership succeeds in silencing Jiang, it would send a powerful message to potential critics about its determination to crush dissent. But Jiang's detention could also trigger a backlash against a party already struggling to maintain its monopoly on power as there is rising social discontent. And if Jiang is not released, he would almost certainly become China's most famous political prisoner.

One senior military official, who spoke on condition of anonymity, said there was broad support for Jiang even within the party and that it will be increasingly difficult for the leadership to hold him as news of his detention spreads. "I consider him a man of honesty and courage," he said. "Ninety-nine percent of the people support him."

Different Explanations

While the government indicated Jiang is being held for violating military regulations, military officials at the No. 301 Hospital of the People's Liberation Army, where Jiang works, have shifted responsibility for his detention to party authorities, a person close to the family said.

The officials told the family that Jiang, a longtime party member, was being investigated for breaking party discipline, the source said. When the family pressed officials to name which regulations Jiang had violated, one of the officials was quoted by the source as replying: "Not being consistent with the party's Central Committee."

The different explanations, and the fact that the authorities have not formally arrested Jiang or charged him with any crime, suggest some uncertainty within the leadership.

The first time Jiang risked his freedom by challenging the government, during the SARS crisis, the leadership also hesitated. But two weeks after his letter to the Chinese media exposing the SARS coverup was leaked to Time magazine, the party fired the health minister and the mayor of Beijing, dramatically raised its official count of SARS cases and launched a mass campaign to alert the public of the disease and stop it from spreading.

Jiang was ordered not to speak to foreign reporters and was put under police surveillance. But within a month, state-run media began publishing articles about him, a few carefully worded reports at first, followed by bolder profiles that praised him as the honest doctor who dared tell the truth about the outbreak.

But the surveillance continued, family members said. And at the end of last year, members of the ruling Politburo Standing Committee discussed Jiang's case during a meeting about ensuring political stability and agreed he should be investigated, a source familiar with the party's decision-making process said.

Then, in late February, Jiang sent a letter to the leadership urging them to admit the party's 1989 military assault on student-led, pro-democracy demonstrations in Tiananmen Square was wrong. While the party has formally acknowledged other errors, including Mao Zedong's destructive Cultural Revolution, it has refused to reevaluate the Tiananmen massacre, in part because doing so might prompt new demands for democratic reform.

In his letter, which was leaked to the foreign press during the March meeting of China's legislature, Jiang recalled what he witnessed on the night of the crackdown, describing how scores of wounded civilians were rushed to the No. 301 Hospital, where he was chief of surgery, and noting that many had been hit by bullets designed to break apart after impact and damage internal organs.

Jiang also said two senior Chinese leaders believed to have played important roles in the crackdown -- the former president, Yang Shangkun, and the party elder Chen Yun -- had suggested in conversations with him or in writing before their deaths in the 1990s that the party would eventually have to admit the massacre was a mistake.

Jiang showed his letter to several friends, and many of them urged him not to send it, arguing it was too dangerous, an associate said. But according to an essay published in Hong Kong by a Beijing dissident who is a friend of Jiang's, the doctor said he wanted to use the political capital he had accumulated during the SARS crisis to speak out on behalf of the victims of the 1989 massacre and their relatives.

Tightened Surveillance

The party's response was immediate. Over the next three months, party and military officials visited Jiang at his home and began summoning him to weekly criticism meetings at the hospital, pressing him to admit making what they called a "serious political mistake" by writing the letter, to explain how it was leaked and to express regret that it was published in the foreign media, sources familiar with the situation said.

Jiang insisted he had followed proper procedures and done nothing wrong. When one of the officials, Zhu Shijun, director of the No. 301 Hospital, challenged Jiang to prove his allegations, the doctor recalled that Zhu had also been in the hospital on the night of the massacre and had witnessed the carnage too, one source said.

The authorities tightened surveillance of Jiang's movements, telephone conversations and e-mail, and required that he seek permission to attend social activities or treat patients at other hospitals, family members said. Security agents questioned all visitors to his home, and when Jiang traveled to western Xinjiang province to treat an old patient, a chaperone was ordered to stay with him at all times.

In May, hospital officials warned Jiang not to go to the U.S. Embassy to apply for a visa to visit his daughter in California until after June 4, the 15th anniversary of the Tiananmen crackdown, a person close to the family said. But Jiang and his wife had an appointment on June 1 at the embassy for fingerprinting, a requirement for visa applicants in China, and requested a car from the hospital.

That morning, the hospital's driver told them the car had broken down and asked them to step into a van with a different driver, the source said. After a short distance, the van stopped. Suddenly, several men surrounded the vehicle, pulled the couple out and shoved them into an armored vehicle with small windows and iron bars, the source said.

On the first day, Jiang and his wife, Hua Zhongwei, were held in different rooms and barred from seeing each other, the source said, but Hua protested by refusing to eat. The next day, security officers moved the couple to another facility and began letting them see each other at least once a day, though always under supervision.

The security officials have forced Jiang to write daily statements and watch videotapes as part of the indoctrination process, sources familiar with the situation said, and they have scrutinized his datebook and other materials for information to use against him. One source described the process as a milder version of the high-pressure, sometimes violent tactics that Chinese security agents have successfully used to force members of the banned Falun Gong spiritual movement to give up their beliefs.

On June 15, several hours after CNN broadcast a telephone interview with the couple's daughter, Jiang Rui, and the Associated Press moved an interview with their son, Jiang Qing, the authorities released Hua. She immediately urged both children to stop talking to reporters, saying she had been told that Jiang's fate would depend in part on their silence, sources close to the family said.

Hua did not return phone calls to her home. One person close to the family said the 72-year-old retired research doctor is terrified and appears to have been traumatized by her experience. Military officials visit her every day to remind her not to speak to reporters, the person said.

Jiang's daughter, Jiang Rui, declined to discuss her father's detention in detail, saying her mother has refused to tell her what happened to them in custody. "Of course, we're very worried about him," she said. "We hope he'll be released soon."

The authorities have not allowed Jiang's family to visit or speak with him and have not said where he is being held. But officials have shown family members at least two handwritten notes from the doctor. In one, the sources said, Jiang said he was fine, urged the family not to worry about him and made the vow to "seek truth through facts."

In the other note, written on June 17, his son's 45th birthday, the doctor said: "Save me a piece of cake."

Military surgeon Jiang Yanyong exposed China's

coverup of SARS. In Beijing, a woman passes a photo of Jiang Yanyong, who is regarded as a hero for exposing the government's attempts to cover up the SARS outbreak.