BEIJING — Human-rights conditions in China deteriorated significantly in 2006, with about 100 activists, lawyers, writers, and academics subjected to police custody, house arrest, incommunicado confinement, pressure in their jobs, and surveillance by plainclothes security forces, a new report by Human Rights Watch said.

Several widely publicized cases involving journalists and rights lawyers were cited in the report as evidence of a severe crackdown, prompted in large part by fears that individual cases of unrest might lead to regional instability. There were 39,000 cases of “public order disruptions,” or large protests, in the first half of 2006, four times as many as 10 years ago, according to data from the Public Security Ministry.

Authorities fired and jailed journalists, shut down more than 700 online forums and ordered eight Internet search engines to filter “subversive and sensitive content” based on 10,000 key words, according to the report, which was released yesterday by the New York-based watchdog group. Lawyers who represented peasants protesting mistreatment were badly beaten, detained, and arrested.

In March, new restrictions were announced requiring protesters’ attorneys to report to local judges in cases involving 10 or more plaintiffs.

In an indication of official attention being paid to perceived agitators, China’s top security chief last weekend toured Shandong province, where a blind legal activist was jailed after exposing abuses stemming from China’s one-child-only policy. A member of the Communist Party’s Politburo Standing Committee, Luo Gan, ordered judicial departments to deal with “discordant elements” at their source.

“Last year, the environment for rights defenders worsened,” a leading intellectual and writer, Liu Shaobo, said. “The government increased its crackdown on lawyers and also its controls on the Internet and the media. I saw more wronged cases last year than in previous years under President Hu Jintao’s governance. And dissidents were under closer surveillance.”

Contributing factors include China’s growing economic power and Washington’s diminished clout with regard to human rights, Kenneth Roth, executive director of Human Rights Watch, said in an introduction to the report.

Mr. Liu said there were some examples of increased openness last year. Newspapers in China’s South were allowed to push the envelope more often than the mainstream state-run press. “Though government enforced controls most of the time, it really wanted to show its open-minded side, especially at the end of the year,” Mr. Liu, whose home is often monitored by police, said.

Analysts have noted that as preparations for the 2008 Olympics continue, officials appear eager to demonstrate that China is modernizing.

The government recently announced that journalists can now travel freely without first obtaining permission from local officials, although they stressed that many local officials might not yet be aware of the new rules.

“On the one hand, they consider rights defenders a challenge to authority and a threat to stability, but on the other hand, they want to build up a good international image for the Olympics,” Mr. Liu said.