OVER THE past week a remarkable exercise in self-government has been taking place in Hong Kong. If China’s rulers were more adept and less insecure, they would embrace the process. Instead they seem intent on delivering another self-inflicted wound.

Despite Chinese objections and cyberattacks, more than 750,000 people — over a fifth of Hong Kong’s registered voters — have cast ballots in the unofficial poll. Organized by a nonviolent protest group called Occupy Central with Love and Peace, it asks residents to choose among three electoral reforms for selection of Hong Kong’s top leader. China, which reclaimed the administrative region from the British in 1997, has steered the selection process of Hong Kong’s chief executive but had promised to allow it universal suffrage by 2017.

Now it seems China plans to stick to the letter, but not the spirit, of its promise. Instead of ensuring true competition, China instead will impose a pro-Beijing committee to nominate candidates for general election, disqualifying anyone who doesn’t “love the country and love Hong Kong.”

China over the past two decades has mostly honored its promise of “one country, two systems,” keeping its hands off Hong Kong’s independent rule of law even as leaders tightened repression in the mainland. And Hong Kong has thrived, its relatively free press and predictable courts drawing international business in a way that Shanghai,for all its success, still cannot.

But there are disturbing signs that China may be rethinking its hands-off policy. A few weeks ago, China released a white paper that asserted its “comprehensive jurisdiction” over Hong Kong. China’s crackdown on courageous mainland dissidents like Liu Xiaobo and Xu Zhiyong has alarmed many residents, who worry that repression could spread. Two major banks, HSBC and Standard Chartered, were allegedly pressured by China to pull their advertisements from two independent Hong Kong publications, Apple Daily and Next. Taiwanese protest leaders were barred from entering Hong Kong.

The result? According to one survey, more than 80 percent of residents aged 21 to 29 feel “dissatisfied” with how Beijing is controlling the island.

Hong Kong residents agitating for self-rule do not challenge the “one country” part of the formula that has been successful until now. They understand they are part of a much larger country with a far different system. By the same token, they hope that China will not see their democratic success as a threat. But the country’s rulers may fear the lesson their people could learn from a successful Chinese democracy more than they care about stifling the lifeblood that is Hong Kong’s freedom.

The United States should be clear that being pro-China means advocating for Hong Kong’s genuine democracy, including allowing a real choice in the nomination and election of chief executive candidates. Anything less will hurt its long-term future.