A new study says China has developed sophisticated methods of blocking what its citizens can read on the Internet. 

The study concludes that Internet users in China are routinely blocked from sites dealing with information on such politically sensitive subjects as Taiwanese independence, the Dalai Lama, Falun Gong, and the Tiananmen Square uprising in 1989.

Researchers from Harvard University, the University of Toronto and Cambridge University in England found that the Chinese government uses government agencies and thousands of public and private employees in a multilayered approach to control access to information on the Internet. 

John Palfrey, executive director of the Berkman Center for Internet and Society at Harvard Law School, was among those leading the study.

"While China seeks to grow its economy through new technologies, the state's actions suggest at the same time a deep-seated fear of the effect of free and open communications made possible by the Internet," he said.  "This fear has led the Chinese government to create what we found to be the world's most sophisticated Internet filtering regime."

Mr. Palfrey says the findings could have implications beyond China.

"China's advanced filtering regime presents a model for other countries with similar interests in censorship to follow," he added.  "Importantly, China now acts as a regional Internet access provider for neighboring states, North Korea, Uzbekistan, Kyrgyzstan, for instance.  Through this important role as a gatekeeper to the Internet for other neighboring states, China may be able to export its filtering technologies."

The study says the tactics used by the Chinese government include blocking certain keywords as well as entire web sites, and demanding that cyber-cafes keep track of users and the Internet sites they visit.

Using tests conducted both inside and outside China, the researchers found that filters were placed on the main backbone networks that carry Internet traffic.   But they also say individual Internet service providers performed their own blocking.  The efforts are done in large part through U.S. hardware and software.

The American companies Cisco Systems, which uses routers to move Internet traffic, and Google Incorporated, which runs the popular search engine, have been accused of supporting China's censorship by shaping their products to fit the Beijing government's needs.

Congressman Dan Burton, an Indiana Republican, is a senior member of the House International Relations Committee.

"I am deeply concerned when I see U.S. firms apparently facilitating Chinese censorship," he said.

Cisco Systems and Google deny the allegations.

U.S. lawmakers are considering steps aimed at countering China's efforts to block access to the Internet, including through tighter export controls and through promoting new technologies aimed at breaking down or circumventing China's Internet controls.

Congressman David Wu is an Oregon Democrat, and also the only Chinese-American in Congress.

"It came to my attention that there are individuals and companies here in the United States which are in the business of cracking the Chinese security systems, and while we should not forget the possibility of impeding the export of control technologies, it may be a much better bang for the buck to invest in those companies that are specifically trying to crack various security systems," he noted.

Meanwhile, Susan O'Sullivan, senior adviser in the Bureau of Democracy, Human Rights and Labor at the State Department, while not responding directly to the new study, said the United States continues to urge China to respect freedom of expression, including on the Internet.

"We attach enormous importance to freedom of expression and the free flow of information into China, so we are raising it all the time," she said.  "Our advocacy on the part of individual prisoners also is an occasion where we raise this because so many of the people we are talking to the Chinese about and seeking the release of are in jail for expressing their views on the Internet or publishing something that got them on the wrong side."

The researchers who conducted the study on Internet access in China are preparing similar reports in the coming months dealing with Vietnam, Iran, Yemen and Singapore.