When Wu Wei's Web site was shut down for the 23rd time, police in the western Chinese city of Chengdu replaced it with one of their own. For a few days last summer, people trying to reach his Democracy and Freedom discussion forum instead found an odd message in large red characters on their computer screens.

"Because this site contains illegal information," the message said, "the webmaster is asked to quickly contact Officer Hu of the Chengdu Public Security Bureau Internet Supervision Department." Helpfully, the officer left a phone number.

Wu, 34, a part-time college lecturer living hundreds of miles away in Guangzhou on China's southeast coast, ignored the request. But users across the country called and berated Officer Hu for closing the site.

Wu said the officer eventually called his cell phone and offered to reopen the site if he turned over data that could help police identify people who had posted essays there.

Wu refused. Instead, he found another company, in another city, selling space on the Internet for personal Web pages. And five days after it was closed, the Democracy and Freedom site was online again.

The authorities have shut down, blocked, hacked or otherwise incapacitated Wu's Web site 38 times in the past three years, repeatedly disrupting the discussions it hosts on political reform, human rights and other subjects the ruling Chinese Communist Party considers taboo. Each time the site has been closed, though, Wu and the friends who help him run it have found a way to open it again.

Their cat-and-mouse game with the country's cyberpolice highlights the unique challenge the Internet poses to the party as it struggles to build a free-market economy while preserving the largest authoritarian political system in the world. It also illustrates how the bounds of permissible speech in China are blurring.

Nearly three decades after the death of Mao Zedong, Chinese enjoy greater personal freedom than ever before under Communist rule, and they routinely criticize the government in private without fear. But people are increasingly using the Internet to broadcast their opinions in public, challenging a key pillar of the party's rule -- its ability to control news, information and public debate.

The party is swift to jail some people who criticize senior leaders or express dissent on sensitive subjects such as Tibet, Taiwan and the Tiananmen Square massacre; at least 55 people are in Chinese prisons on charges related to their Web postings. But others who express the same views go unpunished, because police officers are sometimes apathetic about tracking them down and local Internet businesses are often more interested in attracting customers than enforcing vague rules.

More than 80 million people use the Internet in China, according to official surveys, and the figure has been doubling every 18 months. Unlike authoritarian governments elsewhere, China's rulers have chosen to promote Internet access, aiming to nurture a tech-savvy workforce, stimulate economic growth and improve government efficiency.

But the Internet has become the most unpredictable and difficult to control of the nation's mass media. While Chinese newspapers, radio and television stations are all owned by the state and must follow the party's orders, the country's most popular Web sites are privately owned, driven by profit to expand their audiences and less strictly regulated by government censors. These Web sites are at the cutting edge of an epic struggle unfolding in China today between the authoritarian state and those seeking more freedom.

Several times, the sites have drawn national attention to incidents of perceived injustice, prompting ordinary people to flood the Internet with angry messages. In a country where public demonstrations are forbidden, the government has felt compelled to respond to these online protests. In one case, after an outcry over the death of a young college graduate in police custody, it repealed a decades-old law giving police wide-ranging power to detain people not carrying their residency permits.

Worried about these challenges, the leadership ordered tighter controls on news Web sites this year. The government has also upgraded the technology it uses to block content from overseas and, according to the state media, has begun to install new surveillance software in Internet cafes. Nationwide, China employs an estimated 30,000 people to enforce vague regulations against using the Web to spread rumors, organize cults or disseminate "harmful information."

"The most important battleground for freedom of speech in China is on the Internet now. The authorities realize that, and they are trying to suppress it," Wu said recently, peering at his smudged computer screen and giving a tour of his Web site. "At the same time, we are continuously challenging their bottom line, and pushing them back. . . . This is a critical time."

A New World

A trim man with a wide, square face and large glasses that sit a little too low on his nose, Wu talks fast, with a thick Cantonese accent. His tiny apartment holds only a bed and a small desk for a computer he assembled himself. A plastic cup he uses as an ashtray sits near his keyboard, and newspapers are taped on the only window to keep the sun from overheating the room. The neighborhood is a slum, located far from the college where Wu teaches a class on public administration once a week, and even farther from the factory where his wife works. But the couple chose the room because the rent was cheap and the landlord had wired the building for high-speed Internet access.

The eldest son of party officials, Wu joined the Communist Youth League in middle school and had planned to join the party in college because he believed it was China's best hope for a democratic and prosperous future. But as a freshman, he participated in the pro-democracy demonstrations that swept the nation in 1989, and changed his mind about the party after the Tiananmen massacre.

Wu had his own brush with the power of the state. During the crackdown, party officials demanded he identify teachers who led protests at his university, threatening to kick him out of school if he refused, Wu recalled. After several days of questioning, Wu gave them a name. He immediately regretted it, and decided then he would never give in like that again.

After graduating, Wu was assigned a job in a local office in charge of libraries and bookstores. He was frustrated and bored, until one day in 1998 a colleague introduced him to the Internet. Before long, Wu stumbled onto bulletin board sites hosting lively discussions on history, politics and current affairs. At first, Wu said, he only read what others had posted. But he was drawn into a new world.

When a popular discussion site was shut down in June 2001, he and two doctoral students he met online decided to launch the Democracy and Freedom forum, using a free bulletin board site. "I felt if I didn't speak out, I might not speak forever," recalled Wu, who adopted the Internet name Yedu, from a Tang Dynasty poem describing an empty boat on a river in the wilderness.

The new forum drew hundreds of visitors daily. Wu and his friends moderated debates on such sensitive subjects as President Jiang Zemin's plan to allow entrepreneurs into the party, independence for Tibet and whether China deserved to host the Olympics. Every Friday night, users gathered in an online chat room to continue the discussions in real time.

But less than three months after the Democracy and Freedom forum opened, authorities suddenly shut down the Web site hosting it. Neither police nor the site's managers contacted Wu. He simply clicked on his forum's address one day and saw a message on a white screen indicating the page was unavailable.

Wu and his colleagues set up the forum again on another free discussion site, and it flourished undisturbed for six months. Then, one day, as a group of users planned to meet in person, agents of the Ministry of State Security visited one of Wu's two partners. They pressured him to stop participating in the forum and threatened to withhold his doctoral degree, Wu said. After the student's wife also urged him to stop, he agreed to quit.

"We all could understand his decision," said Wu, whose own wife has urged him to give up the Web site. "People have to make their own choices."

Over the next six months, the authorities shut down Wu's forum 12 times. On a few occasions, the entire Web site hosting it would disappear. Other times, only his forum was closed, replaced by a message that said, "This forum has already been deleted."

Wu said he was not afraid back then because the government had not yet arrested many people for Internet activities and because he believed he was doing nothing illegal. "I mainly felt angry," he recalled. "We had freedom of speech on the Internet, but now the authorities wouldn't even let us have that space."

Still, Wu began taking precautions. When posting his own essays, he used a software program that allowed him to sign on to the Internet through a proxy server, making it difficult if not impossible for the authorities to track him down.

Despite the shutdowns, his forum continued to attract new users. Each time it closed and opened, Wu sent out a mass of e-mails with its new location, and flooded the Internet with similar notices.

Then, in November 2002, police in Beijing arrested two of his site's regular essayists. The same day, Wu's supervisor at the library and bookstore oversight office accused him of keeping "extremely reactionary essays" on his office computer and suspended him pending a party investigation.

For the first time since setting up the site, Wu was frightened and nervous. He was ordered not to leave his home. "Any time an individual faces the huge state organ, you feel alone and weak," he said. So he stayed off the Internet.

As the months passed, his friends online grew anxious. "We were worried he might have been arrested," recalled Mou Bo, 28, a medical student in Shanghai and one of the site's co-founders. But Mou and others kept the forum running.

In the end, the officials investigating Wu never asked about his Web forum or inspected his home computer, which he used to manage it. Instead, he recalled, they examined the essays he had downloaded at the office from dissident Web sites overseas. That was enough for him to lose his job.

Thriving Underground

In April 2003, after moving to Guangzhou in search of work, Wu finally signed on to the Internet again. To his surprise, the Democracy and Freedom forum was thriving. Authorities had not shut it down in months. Wu said police appeared distracted by the SARS crisis.

The next time police shut down the site, in May 2003, Wu and his friends changed tactics. Instead of moving to another Web site hosting discussion forums for free, they decided to design a site of their own and rent space from an Internet service provider. More people could sign on simultaneously, and the discussions could be expanded and organized. Most important, they would be able to save a copy of the site so the material would no longer be lost every time authorities pulled the plug.

They named the main forum the Sound of Freedom and set aside another section to mark the 15th anniversary of the Tiananmen Square massacre. They also began offering downloads, including the texts of banned books and a variety of video and audio files. Among the recent offerings was footage of the huge anti-government protests in Hong Kong last year and a bootleg copy of the movie "1984," based on George Orwell's novel.

One page on the site, titled "Freedom of Speech is Not a Crime," highlighted the danger of their endeavor. It listed the names of 20 people jailed for expressing their views on the Web, including several who were regular essayists on the site. Wu never deleted their writings after the arrests. Unlike the hosts of most Chinese Web sites, he has also refused to employ a software filter to block messages with sensitive phrases such as human rights.

A dozen other friends scattered across 10 provinces were helping Wu and Mou now. They were civil servants and computer programmers, entrepreneurs and scholars, even a government official and a well-known novelist, all using Internet pen names. Only a few had ever met. Instead they communicated using Microsoft's free instant messaging system, which allowed them to hold conversations and meetings online.

They rented Web space, available in China for about $15 a month, and the new site debuted in June 2003. Two days later, it was shut down. The Internet firm explained that police in Beijing ordered them to do so, Wu said.

Wu and his partners tried again with an Internet firm in Chengdu a few weeks later. The site stayed up about two months before the message from Officer Hu appeared.

Over time, a pattern emerged. Wu used the Google search engine to find a company renting Web space on a monthly basis and using software compatible with his. The process involved clicking on link after link, and could take days. Then he contacted the firm by instant messaging, and a partner would send the payment electronically.

The company usually put up the Web site immediately, without asking questions. Then, within a few weeks, it would shut it down. Often, an employee warned that police had ordered the closure and launched a criminal investigation.

But only once did police follow through and question Wu or his colleagues. Last September, police in Jiangsu province detained the Web manager from Wu's site who had contacted and paid the last Internet firm. At about the same time, officers from the Ministry of State Security detained another of the site's managers.

Wu and the others prepared for the worst. They stopped trying to rent Internet space. They also destroyed personal letters and meeting notes that might be used against them or their friends.

As he waited, Wu began rereading essays written by dissidents who had spent time in prison. "This was the most tense time," he recalled. "We had already lost several Internet friends. We knew what was possible."

But then his two partners were released. Days and then weeks passed without a knock on his door or word of any other arrests. Eventually, Wu and his friends concluded they were safe. And they began renting Internet space again.

Eluding the Police

As time passed, Wu and his colleagues came to a series of surprising conclusions about the men and women shutting down their Web site.

First, the Internet service providers didn't seem to care until police stepped in. State regulations require the providers to monitor the sites they host, save data about the users who visit them and ensure that discussion sites are registered with the government. But the companies appeared more interested in winning customers than screening them.

There was a pattern to the behavior of the police too. It would have been possible to track down Wu and his partners, given the electronic trail they left by renting the server space and using it regularly. But the police didn't seem interested. The officers were usually in the same city as the Internet service provider, and they rarely left the jurisdiction.

It also would have been easy for the authorities to shut down the site quickly. Wu gave out the new address to anyone who asked. But the site often stayed open for weeks before police acted.

"The party is not a monolithic block," Wu said. "The police may feel, 'If we can avoid the trouble, let's avoid the trouble.' No one wants to go out of their way to hurt people."

Many officers and officials appear more concerned about profiting from the Internet than policing it. For example, a campaign to regulate Internet cafes has faltered because local authorities often look the other way when cafe managers fail to record customers' names or install surveillance software, as long as they pay taxes and fees.

"There are more and more of us mice, but the cat, for various reasons, is less interested in its work," said one of Wu's partners, a woman who helps manage Shanghai's economy. Another partner, a computer technician in Nanjing, added, "The cat is too busy making money."

'We're Not Going to Stop'

Wu said he cannot compete with the government's resources or its access to high technology. When he attempted to establish the site on a server overseas last year, for example, the authorities blocked users in China from seeing it. But Wu said he and his friends are more committed to their cause.

In December, they took the fight to a new level, organizing a petition drive on the site for the first time. Wu drafted an open letter calling for the release of Du Daobin, a regular writer on their site who had been arrested and charged with "inciting subversion against the state" after posting essays supporting last year's protests in Hong Kong. "This is a case of criminalizing speech," Wu wrote, urging the government to clarify the nation's subversion laws and stop using them to "suppress the people from carrying out peaceful criticism."

Wu circulated the petition among liberal intellectuals and legal scholars, who made improvements, then posted it on his site on Feb. 1. Police were slow to respond, and it quickly drew more than 1,400 signatures.

About two weeks later, Wu noticed that someone had deleted pages from the online petition. Then people began to have trouble accessing other pages on the site. Messages appeared telling users that essays were inaccessible because they contained "illegal phrases." Some indicated "Communist Party" was an illegal phrase.

On Feb. 19, the site was shut down. The Internet firm hosting it said it had acted under orders from the Ministry of State Security. Since the beginning of March, the site has opened and closed five more times.

"We're not going to stop," Wu vowed. "We'll try again in a few days."

Wu Wei, 34, manages the Democracy and Freedom Web site from his tiny apartment located in a slum in the southeastern Chinese city of Guangzhou.