With lights ablaze and news cameras rolling, professional Web surfer Fang Nan sat before his Chinese government-issue Compaq Presario computer this afternoon, pointed his Microsoft Internet Explorer browser to an Internet address in the United States and began downloading sophisticated technical details about advanced U.S. nuclear warheads.

The demonstration, put on by China's State Council, or cabinet, was part of the government's most aggressive attempt yet to discredit an American congressional report released last week that accuses China of stealing U.S. nuclear secrets during the past two decades.

Zhao Qizheng, spokesman for the State Council, repeated China's long-standing insistence that it has never stolen American nuclear technology. He also leveled accusations of racism and arrogance at Rep. Christopher Cox (R-Calif.) and the other members of a bipartisan select committee, saying their report was an effort to diminish the outstanding work of China's bomb and missile makers, who need no help from the United States.

But Zhao went beyond the standard denials, telling Chinese and foreign reporters that the information China is accused of stealing -- including critical design information on the W88 warhead and six others -- has long been openly available in the United States. He cited in particular the Nuclear Weapons Databook series published by the Natural Resources Defense Council.

"Moreover, in recent years, performance data about various types of nuclear warheads, ranging from the early MK-1 [the type of weapon used against Hiroshima in 1945] to the latest W88, can easily be found on the Internet," he said. "They are no longer secrets, so there is nothing to steal."

Zhao refused to answer any questions before relinquishing the stage to Fang, of the China Internet Information Center, a government body that tracks Internet activity in China.

Fang logged on to the Internet and immediately bounced to the Web page of the Federation of American Scientists, a Washington-based group concerned with weapons proliferation and other issues. The federation was founded by scientists who worked on the Manhattan Project and disseminates detailed information on nuclear weapons to encourage public debate on disarmament.

The results of Fang's efforts, including a list of every U.S. nuclear weapon and its specifications, were projected on a large screen. He then searched for W88. Up popped the explosive yield, weight, length and diameter of the warhead, as well as a description of the specific materials used and its key design features.

Fang said he and several other Internet buffs thought of searching for nuclear information on the Internet after reading the Cox report last Wednesday. They also found academic bulletin boards used by American scientists to be great sources of detailed information on U.S. nuclear weapons, he said.

Charles Ferguson, a senior research analyst at the federation and a nuclear expert, said the information on his organization's site could be useful to China. But he disputed the suggestion that there is no difference between what is available in public and secret information.

The site provides "a wealth of information on nuclear weapons, but we don't have a manual for how to produce them or anything like that," Ferguson said.

"There are thousands of parts in the most advanced nuclear weapons," he added. Just knowing "the basic components, what goes into the primary part of it, what goes into the secondary part of it . . . is not enough to give someone the blueprint to develop these things."

CAPTION: Computer engineer shows reporters how to find information about U.S. weapons on the Internet.