By Jonathan Krim

The Chinese government is succeeding in broadly censoring what its citizens can read on the Internet, surprising many experts and denting U.S. government hopes that online access would be a quick catalyst for democratic political reform.

Internet users in the world's most populous country are routinely blocked from sites featuring information on subjects such as Taiwanese independence, the Falun Gong movement, the Dalai Lama and the Tiananmen Square uprising in 1989, according to a study to be released today by a consortium of researchers from Harvard University, the University of Toronto and Cambridge University in England.

The study, which evaluated China's Internet practices over the past year, found the government employed an aggressive array of tactics, including blocking certain keyword searches and whole Web sites, and forcing cyber-cafes to keep records of users and the Web pages they visit.

"China operates the most extensive, technologically sophisticated and broad-reaching system of Internet filtering in the world," the study said.

Researchers said they worry that China's censorship system could become a model for other countries looking to keep the lid on Internet use.

China's success at censorship is even more remarkable to researchers because the country is promoting economic growth using technology. An estimated 100 million Chinese use the Internet, nearly half of whom who have high-speed connections.

"The Chinese are successfully developing a market economy at the same time they are continuing to accomplish control over the Internet and the media," said C. Richard D'Amato, chairman of the U.S.-China Economic and Security Review Commission, which monitors and promotes economic progress in China.

D'Amato said the jury "is not only out, it's way out" on whether the Internet is playing the democratizing role the United States had hoped.

The study also undermines the popular notion that the Internet is an organism that is difficult to tame.

"The Internet is wildly misunderstood," said Rafal Rohozinski, director of the Advanced Network Research Group at Cambridge, who participated in the study. "It is built around very specific chokepoints" that can be controlled.

Using tests conducted inside and outside China, researchers were able to identify censorship at many of those points.

Filters are placed on the main "backbone" networks that carry Internet traffic, the study said. A handful of licensed Internet providers also perform their own filtering. Major Chinese search engines filter out or block keywords that would enable surfers to see certain sites. Providers of Web log, or blogging, services block certain posts. Text messaging software has built-in forbidden lists of keywords, which halt service temporarily if used.

Chinese authorities perform these tasks largely using U.S. hardware and software.

For example, Cisco Systems Inc. routers, machines that move Internet traffic around, are capable of recognizing individual portions of data, a technology that helps battle worms and viruses. That same technology can be used to distinguish certain content.

Companies such as Cisco and Google Inc. have been accused of aiding China's censorship by tailoring their products to suit the government's needs. The study did not confirm those allegations, which the companies have denied.

Some reports on Chinese censorship also claim that the country has as many as 30,000 "Internet police" dedicated to the task, but the study did not confirm that estimate. Still, it identified 11 government agencies that share responsibility for controlling Internet use in the country.

Despite wholesale blocking of Web sites dedicated to news on Taiwan or Tibet, for example, Chinese surfers still can get access to many Western news and culture sites.

Researchers said the filtering efforts seem to shift regularly, so that at certain times a CNN site on Tiananmen Square was accessible, for example.

Rohozinski said the censorship efforts seem to primarily target sites written in Chinese.