There are quiet moments with his 4-year-old son at his apartment in the suburbs when Zheng Xuguang manages to forget the event that changed his life 15 years ago: the violent crackdown on pro-democracy demonstrations in Tiananmen Square.

He was a leader of the student protests, No. 9 on the government's "most-wanted" list, but he withdrew from dissident politics soon after leaving prison. He lost a series of jobs because police harassed his employers. He then decided to stay home and earn a living by playing the stock market.

Yet Zheng can't escape the memories: the exhilaration of marching through the city with a crowd of hundreds of thousands; the horror of a tank crushing a friend's legs; the pallor of a student's body carried out of a hospital on a wooden board; the voice of the doctor who told him 45 other bodies had already been taken away. Fifteen years ago Friday, the ruling Communist Party sent troops to end weeks of peaceful protests in Tiananmen Square, killing hundreds, perhaps thousands, in an act of violence that China has yet to fully recover from.

At the time, the government issued a list of 21 most-wanted student leaders. Today, most of them have fled or been sent into exile in the United States or Europe. But Zheng is one of seven still living in China under the same authoritarian government that they protested against and that ordered its soldiers to fire on them. Their stories offer a lesson in how China has learned to live with what happened in Tiananmen Square, but without forgetting or forgiving.

The government has labored to put the June 4, 1989, massacre behind it, suppressing public discussion of the event while highlighting the rapid economic growth China has achieved in the years since. But the memory of Tiananmen continues to mar China's reputation abroad, and at home it remains a powerful symbol -- and potential rallying point -- for those dissatisfied with the Communist Party's monopoly on power.

The party defends the Tiananmen crackdown as necessary to maintain stability, and it has resisted calls to reassess its decision to send in troops. It has formally acknowledged errors before, including Mao Zedong's destructive 1966-76 Cultural Revolution, but Tiananmen is particularly sensitive because a reversal could prompt fresh demands for democratic reform. Earlier this year, the party began requiring officials to watch a four-hour documentary defending the crackdown, the Reuters news agency reported Thursday. And the Chinese leader ousted in 1989 for opposing the crackdown, Zhao Ziyang, remains under house arrest at age 84.

In recent weeks, the government has detained or placed under surveillance dozens of dissidents and relatives of those killed in 1989, as it does every year to prevent any commemoration of the June 4 anniversary. Among those who appear to have been detained is Jiang Yanyong, 72, a military surgeon who became a national hero after helping to expose the government's coverup of the SARS outbreak and who wrote a letter this year calling on the government to admit its error in ordering the Tiananmen crackdown.

In addition, human rights groups have identified about 125 people still in prison on charges related to their participation in the protests, mostly workers who rallied behind the students. The total number behind bars is estimated to exceed 500.

One of the seven student leaders still in China, Yang Tao, 34, was arrested again in May 1999 on subversion charges for attempting to mark the 10th anniversary of the massacre. He was released last year after completing a four-year sentence, but declined an interview request. A friend said that police had ordered him not to speak to reporters and that he was worried about how he would support his elderly father if he were arrested again.

Another of the student leaders, Wang Zhixin, 36, also said it was inconvenient for him to be interviewed. But four others agreed to discuss their lives since the crackdown, including two who asked to be interviewed by telephone because they were under police surveillance.

All of them said they had been barred from returning to college after being released from prison in the early 1990s and have had difficulty finding steady work because many people are afraid to hire or do business with them. They said police have also harassed their employers and warned not to give them promotions.

"I have a lot of spare time, so I often think about what happened," Zheng said recently, sitting in an armchair at home with his son in his lap. "Since 1995, I stopped participating in political activities. You might say I've been acting against my conscience. . . . I've been making some money, but my heart still feels the pressure from 1989."

Zheng, 36, a soft-spoken man with a long face, spent two years in prison for "assembling a crowd to disrupt traffic" in Tiananmen. He said he was consumed with anger when he was released. "I felt that if this murderous government wasn't overthrown and killed, I would never be mentally at peace," he recalled.

But then he made contact with old friends and found comfort in dissident politics, signing petitions, organizing a campaign on behalf of residents whose houses were being demolished and attending discussion forums on democratic reform.

Police detained him twice, holding him for several weeks each time and beating him once, he said. The authorities also ruined his wedding, warning all his friends not to attend. Then in 1995, after police pressured a trusted colleague into denouncing him in public, Zheng decided to abandon politics. "I didn't have a source of income," he said, "and I needed to make money."

Zheng said he is in debt now but no longer as worried about his finances because his stocks have done well. The volumes on political philosophy on his bookshelves were replaced by the translated works of Warren Buffett. But he wrestles with his conscience about whether he should be doing more on behalf of those who died at Tiananmen. His wife said he still has nightmares.

"I do feel guilty," he said. "If a student doesn't appeal on behalf of the students who died, how can you not feel guilty?"

Ma Shaofang, who was No. 10 on the most-wanted list, said he also struggles with pangs of guilt, about what happened 15 years ago and about not doing enough since. Reached by telephone in the southern city of Shenzhen, he said the government bore ultimate responsibility for the bloodshed in 1989, but he and the other students might have saved lives had they been more willing to compromise with the authorities.

Ma, 39, said he was haunted by the memory of a small child he saw who had been shot several times. "I feel responsible for that child's death," he said. "I could have done better in 1989, and I could have done more afterward."

After he was released from prison, Ma said he refrained from politics, only occasionally signing a petition or writing an essay. But the police have made it difficult for him to make a living. He said he started his own brand marketing firm in 2001, but the authorities frightened off all his customers last month.

"I used to think I should stay out of politics, because if I couldn't solve my own problems, how could I solve society's problems?" he said. "Now I realize I can't solve my own problems because the police are always harassing me. I realize that I just want to be an ordinary citizen, and to be a citizen, I have to assert my rights and speak out."

Wang Zhengyun, No. 8 on the most-wanted list, said he also has struggled to make a living. A member of China's ethnic Lahu minority, he grew up in an impoverished mountain village in Yunnan province and was among the first from his village to go to college. But after Tiananmen and a prison term, the authorities forced him to go back to the village.

A year later, Wang returned to Beijing. He said he lived in basement apartments and survived by selling stones for use in construction. Then he saved enough to open a store to sell home audio equipment. Eventually, he opened a chain of stores and last year started a firm that wires buildings with audio, video and computer cables. But Wang, 35, said he still feels "a dull pain, spiritually."

"I wish I was able to do something for China's democratization," Wang, a wiry man with a buzz cut and an angular face, said over lunch this week. "Who wants to accept a government that gives you no hope and no freedom? . . . But what can we do? What's the next step? I don't know."

Until recently, the most successful of the student leaders who stayed in China was Zhang Ming, No. 19 on the list. After his release, Zhang avoided his fellow students and stayed away from politics. He even changed his name.

"He had already suffered tremendously, and he wanted to concentrate on economic development," said John Zhang, his younger brother, a software engineer. "He decided that would be how he would contribute to the country."

John Zhang said his brother found a partner, and over the past decade they built a huge real estate conglomerate in Shanghai with subsidiaries in the software, mobile telephone and auto industries and nearly $250 million in assets. But in late 2002, state security agents arrested him and accused him of planning to blow up a building. The charge was later changed to embezzlement, and he was sentenced to seven years in prison.

Zhang said a business rival used his brother's Tiananmen background to persuade local party authorities in Shanghai to crush him. Zhang Ming, 39, is now on a hunger strike in prison.

Zhai Weimin, No. 6 on the list, also complained of official harassment and said he would leave China if he could. "I feel like I'm living in a big net. It's very stifling," said Zhai, 36, by telephone from his home in Henan province, where his small publishing business is struggling.

But Zhai said he never feels lonely. Local residents remember what he did 15 years ago, he said, and they often seek him out for help in addressing grievances with the government and local businesses. "People haven't forgotten June 4," he said. "Their feelings may be less intense and they may be scared, but they haven't forgotten."

Zheng Xuguang, holding his 4-year-old son, spent two years in prison for helping lead the Tiananmen Square protests. In a famous photo, a Chinese man stood alone to block a line of tanks heading to put down pro-democracy demonstrations in Tiananmen Square. "I wish I was able to do something for China's democratization," protest leader Wang Zhengyun said of life after Tiananmen Square. Zhang Ming built a hugely prosperous real estate business in the years after the protests but recently was sent back to prison.