When 10 policemen barged into the Beijing apartment of Hu Jia and Zeng Jinyan last Friday morning and told them that they were under house arrest and prohibited from leaving the country, it was more than just the latest incident in a long-standing crackdown against human-rights activists. It was also an indication of how China intends to handle dissent between now and the Olympic games that will open in Beijing in August 2008.

Mr. Hu and Ms. Zeng, who are expecting their first child in September, are the most prominent figures of a new generation of rights activists in the mainland. They take the Chinese government's promises at face value, insisting that provisions protecting rights in China's constitution and laws be upheld. And they are savvy about how to put pressure on the government, aware that the Olympics provide a once-in-a-lifetime opportunity to put China's abysmal rights record under the international spotlight.

Mr. Hu started in Beijing as an HIV/AIDS activist a decade ago, and quickly came to realize that without freedoms of speech and press, China's nascent civil society would never be a serious actor in addressing China's many social challenges, such as its acute environmental crisis, the lack of a social safety net for the poor, and the HIV/AIDS epidemic. Mr. Hu soon became one of the primary advocates for other activists facing jail or threats, relaying information to Chinese citizens and the outside world. For this, he spent more than 200 days under house arrest last year; this followed detention for over a month the previous year -- a period in which the police never informed Ms. Zeng about her husband's whereabouts.

Ms. Zeng has also become a noted human-rights activist since her husband's arrest. She started blogging about Mr. Hu's disappearance and later about their 200 days under house arrest, and quickly attracted a large following. Together, they made a 31-minute documentary about their ordeal, "Prisoner of Freedom City," which shows on camera for the first time the harassment that dissidents and critics are subjected to by state security personnel. Her blog has now been blocked in China, but is still available abroad. Recently, she was named by Time magazine as one of the World's "100 most influential people."

When they were placed under house arrest last Friday, Mr. Hu and Ms. Zeng were minutes from leaving for a two-month trip to Europe, where they intended to speak about the human-rights situation in the run-up to the Olympics and to screen their documentary in various national capitals. Instead, the police took Mr. Hu to the police station for four hours of interrogation, telling him that he and his wife were suspected of "harming state security" -- the kind of ill-defined charges often leveled against dissenters.

Preventing government critics from traveling abroad is becoming a regular feature of China's repressive tactics. In February, 20 mainland writers were prohibited from traveling to Hong Kong for a major conference organized by PEN, an international writers association. In March, the authorities tried to prevent 80-year old HIV/AIDS activist Dr. Gao Yaojie from going to the U.S. to receive a human rights award (they did an about face when this provoked an international outcry). In April, five rights activists from Beijing, Chongqing and Wuhan were prevented from traveling to a legal conference in Hong Kong. In these instances, as in Mr. Hu and Ms. Zeng's case, the police provided no legal basis whatsoever for their order.

Indeed, there is no basis under Chinese law for ruanjin. Literally meaning "soft arrest," ruanjin is imposed at the complete discretion of the police, outside of any legal procedure. Ruanjin subjects one's daily life to the whims of the secret police. In practice it means 24-hour surveillance by unidentified and often aggressive police officers, confinement at home, and restricted and monitored telephone and Internet communications. When a foreign diplomat tried to visit Mr. Hu last year, the police sealed off the entire housing block and turned the visitor away.

Unfortunately, Mr. Hu and Ms. Zeng's case isn't unique. Chinese rights activists are routinely put under house arrest. It is a life in limbo: One never knows when it will come and when it will end. It can last a long time, as it has for Liu Xiaobo, the famous Beijing writer and dissident who has endured ruanjin on and off for over a decade.

Despite the large number of security officials ruanjin entails, with often dozens of law-enforcement personnel mobilized on a single person or family for months, for the Chinese authorities "soft arrest" presents several advantages over formal arrest and jailing. Putting a dissident in prison attracts greater attention and condemnation from the international community. Formal charging and jailing of activists for expressing their opinions also gives the lie to China's promise to make improvements in the human rights situation before the Olympics. House arrest, on the other hand, attracts less notice, while still intimidating countless others.

The Olympics may be a year away, but the government's efforts to silence critics are already in full swing. There is little reason to think the wave of arrests will slow -- if anything, they'll accelerate as opening day approaches. The international community isn't powerless; countries participating in the Olympics, and the Olympic committee itself, can lodge protests and lobby to prevent future arrests. At the very least, no one can sit quietly when critics and human-rights defenders are silenced in this way.

Brad Adams is Asia director at Human Rights Watch.