Chinese writer and activist Li Tie was sentenced to 10 years in prison for “inciting subversion,” his family members said Thursday. Li is the third high-
profile dissident handed a lengthy term in the past few weeks, part of a Communist Party crackdown ahead of a scheduled leadership change this year.

Like two activists sentenced last month, Li was prosecuted for essays he posted on the Internet demanding greater democracy. The convictions indicate that the government in Beijing sees online treatises — and the followers they might garner — as a serious threat to China’s political and social stability.

Li, from Wuhan city in Hubei province, was sentenced Wednesday, his family members said. He was not allowed to hire a lawyer.

Human rights groups outside China say the three recent sentences far exceed those normally given in such cases and perhaps reflect official nervousness about the first anniversary of the Middle East uprisings known as the Arab Spring, which prompted shadowy Internet calls for similar protests in China.

On Dec. 26, a court in Guizhou province sentenced a veteran human rights campaigner, Chen Xi, to 10 years in prison. Three days earlier in Sichuan province, activist Chen Wei was sentenced to nine years. Both were convicted of “inciting subversion of state power.”

Another activist, Zhu Yufu, was charged this week with the same crime after he posted a poem online titled “It’s Time,” which urges the Chinese people to stand up for their freedoms.

This is a crucial year for China’s ruling Communist Party, which is preparing for the first top-level leadership changes in a decade. Analysts say authorities are worried about anything that could disrupt the carefully choreographed shuffle in which Vice President Xi Jinping is slated to take over as general secretary of the party and, later, as the country’s president.

Leadership changes are typically closed-door affairs in China, with the new general secretary and the powerful nine-member ruling Politburo Standing Committee introduced onstage at an autumn Party Congress in Beijing once all the backroom dealmaking is complete. Ordinary Chinese citizens play no part, other than as spectators.

But this will also be the first leadership change to take place in an age when tens of millions of Chinese feel empowered to speak out through the hugely popular Twitter-like microblogging sites collectively known here as “weibo.” The weibo sites have given many Chinese a source of once-censored information and a new outlet for voicing opinions once deemed too sensitive even to whisper in public.

Recent official statistics from the China Internet Network Information Center showed there are now 513 million Internet users in the country of 1.3 billion people. The number of microbloggers quadrupled in 2011, to 250 million.

This week, authorities signaled that they are trying to bring that relatively freewheeling microblogging world under tighter control. A handful of eastern cities, including Beijing and Shanghai, have been experimenting with a pilot program that requires people signing up for weibo accounts to register with their real names and identity card numbers, making it easier to trace them if they post something the government doesn’t like.

Wang Chen, the State Council information minister, said Wednesday that the pilot program will be extended nationwide and made retroactive to people already microblogging under nicknames and pseudonyms.

An official with a company that hosts a popular microblogging site predicted that real-name registration, when fully implemented, will have a “chilling effect” on what people are willing to post online. He also said the government probably would not try to shut down the popular microblogging sites altogether, for fear of sparking a backlash.

Another prominent Chinese writer and dissident held a news conference in Washington on Wednesday and described how he was allegedly harassed, abducted and tortured by Chinese security forces, and later forced to flee with his family to the United States. The writer, Yu Jie, is the author of a critical book on China’s prime minister, “China’s Best Actor: Wen Jiabao,” which was banned in China. He said he is completing another book, on China’s president, called “Hu Jintao:Cold-Blooded Tyrant.”

China has also been dealing with continuing unrest among ethnic Tibetans, and there are signs that a protest movement is spreading. There have been 17 reported cases of Tibetans — monks, nuns and ordinary people — setting themselves on fire, including at least three cases this year.

The U.S. ambassador to China, Gary Locke, said Monday on PBS’s “Charlie Rose” show that the human rights climate in China is “in a down period, and it’s getting worse.” Locke mentioned the Arab Spring uprisings, including the revolutions in Egypt and Libya, and said: “The Chinese leaders are very fearful of something similar happening within China, so there’s been a significant crackdown on dissension and political discussion, even the rights and the activities of lawyers. . . . There’s a significant crackdown and repression going on within China .”

A foreign ministry spokesman, Liu Weimin, sharply criticized Locke’s comments as “not the truth.”

“China’s progress in human rights is obvious to all,” Liu said. “We are willing to work with the international community on human rights issues. But we object to interference in China’s internal affairs and the violation of China’s judicial sovereignty by making an issue of human rights.”