BEIJING — Google, facing an assault by hackers who sought to penetrate the e-mail accounts of Chinese human rights activists, will stop cooperating with Chinese censorship and consider closing its offices and operations in China altogether, the company said on Tuesday.

The abrupt departure would be a startling end to Google’s foray into a country with more than 300 million Internet users. Since arriving here in 2006 under an arrangement with the government that purged its Chinese search results of banned topics, Google has come under fire for abetting a system that restricts what its citizens can read on the Internet.

Google said it was unclear who orchestrated the attacks on its systems but described them as “highly sophisticated” and said they included an assault on at least 20 other companies in the finance, technology, media and chemical sectors.

The primary goal of the hackers, the company said, were the Gmail accounts of human rights activists, although none of the targeted accounts were breached.

Google did not publicly link the Chinese government to the cyberattack, but people with knowledge of Google’s investigation said they had enough evidence to justify its actions.

The company said the attacks originated within China, which has long constrained the search engine’s results and presented a challenge to the company’s guiding zeitgeist, “Don’t be evil.” The company said it would try to work out an arrangement with the Chinese government to provide an uncensored Internet — a tall order in a country that heavily filters the Web — but that it would close its offices in China if its demands were not met.

“We have decided we are no longer willing to continue censoring our results on Google.cn, and so over the next few weeks we will be discussing with the Chinese government the basis on which we could operate an unfiltered search engine within the law, if at all,” David Drummond, a senior vice president of corporate development and chief legal officer, said in a statement.

Weighing the consequences

Wenqi Gao, a spokesman for the Chinese Consulate in New York, said he did not see any problems with Google.cn. “I want to reaffirm that China is committed to protecting the legitimate rights and interests of foreign companies in our country,” he said in a phone interview.

In China, search requests that include words such as “Tiananmen Square massacre” or “Dalai Lama” come up blank. In recent months, the government has also blocked YouTube.

Google’s apparent decision to play hardball raises enormous risks for the company. While Google’s business in China remains small for now, analysts say that the country could soon become one of the most lucrative Internet markets.

“The consequences of not playing the China market could be very big for any company, but particularly for an Internet company that makes its money from advertising,” said David Yoffie, a professor at Harvard Business School.

At the time of its arrival, the company said that it believed that the benefits of its presence in China outweighed the downside of being forced to censor some search results there, as it would provide more information to Chinese citizens. But it has repeatedly said that it will monitor restrictions in China.

‘Enough is enough’

Google’s announcement drew praise from free-speech and human rights advocates, many of whom had criticized the company in the past over its decision to enter the Chinese market despite censorship requirements.

“I think that with the increasing demands that were being placed on Google vis-a-vis censorship, combined with these very troubling cyberattacks, Google reached a tipping point,” said Leslie Harris, president of the Center for Democracy and Technology, an advocacy group based in Washington, D.C. “It is a principled decision.”

Rebecca MacKinnon, a former CNN reporter and an expert on the Chinese Internet, said Google had endured harassment in recent months and that by having operations in China it potentially put at risk the security of its users there. “Unless they turn themselves into a Chinese company, Google could not win,” she said. “The company has clearly put its foot down and said enough is enough.”