A CHINESE blogger named Wu Dong became an Internet star last year by tracking and reporting on the luxury watches worn by the country’s senior officials. One of the Communist Party bosses he singled out was arrested and sentenced to prison this month. But Mr. Wu himself was reported to be under arrest Tuesday — the latest victim in a mounting crackdown by China’s new leaders on those who advocate political reform or speak out on social media.

Xi Jinping, who took over as party chief last November, has tried to bolster his popularity by waging a campaign against corruption and adopting some of the rhetoric of Maoist leftists. But as a slowdown in growth exposes deep-rooted problems with China’s economic model, the new leader increasingly is turning to repression to silence real and potential opponents. Human rights groups say more than 50 activists have been jailed since Mr. Xi assumed the presidency in March, including businessmen, academics and journalists.

Many are people whom Mr. Xi could and should have regarded as allies in an effort to open the political system. One is Wang Gongquan, a well-known businessman and member of the New Citizens Movement, a campaign to promote the rule of law and citizens’ rights. He was arrested Friday and charged with “organizing a mob to disturb public order” — which is the regime’s way of describing a small demonstration in Beijing that called for senior officials to disclose their assets. Mr. Wang was the third leader of the New Citizens Movement to be arrested since July, including founder Xu Zhiyong.

Authorities are, meanwhile, engaged in a campaign to stifle free speech on the Internet. A judicial ruling last week stipulated that bloggers could be sentenced to three years in prison for “spreading rumors” if their reports are reposted more than 500 times or viewed by more than 5,000 people. On Sunday, state television broadcast a chilling video of a Chinese American businessman renouncing postings on the Chinese version of Twitter that had gained him 12 million followers. The blogger, Charles Xue, was arrested on charges of soliciting a prostitute; his meek confession and self-criticism echoed the public humiliation of intellectuals during the Cultural Revolution.

The wave of repression is counterproductive in more ways than one. In addition to advocating incremental and peaceful reforms to the political system, the activists being targeted have been instrumental in calling attention to corruption and other abuses the Communist Party must address to avoid more serious unrest. It’s not just luxury watches: microbloggers have helped to force action on food safety and air pollution, among other issues.

Mr. Xi’s turn to repression has gone almost entirely unremarked upon by the Obama administration, which has concentrated on cultivating relations with the new leader. This, too, is shortsighted. It’s in the interest of the United States that China continue on a path of stable development, and intensified repression is more likely to crack open an increasingly restless society than to contain it. As Mr. Wang told The Post’s Simon Denyer recently, “If the government does not open society, it will cause more hurt and more violence, which is not in the government’s interest, either.” President Obama should be making that point to Mr. Xi — and letting the country’s reformers know the United States is on their side.