By Jeffrey Parker

BEIJING, Sep 2 (Reuter) - Intrusive Chinese security, including surveillance and restrictions on free speech, is threatening the world women's conference and must be addressed by the United Nations, the U.S. delegation said Saturday.

"I think that the Chinese are going to find that if they continue this they are going to find themselves making the conference extremely difficult," Timothy Wirth, U.S. undersecretary of state for global affairs and senior member of the U.S. delegation, told a news briefing.

Wirth said the security issue, already boiling into controversy at the Non-Governmental Organizations (NGO) forum running in tandem to the U.N. World Conference on Women, would become a major focus at the main conference center in Beijing next week.

Chinese security officials have been deployed in large numbers to follow and videotape NGO forum participants known to be critical of Chinese policy on human rights, Tibet and other sensitive issues, monitoring their movements and contacts.

Wirth said he had noticed he was being subjected to obvious surveillance and was aware foreign reporters covering the meetings were also being followed. He said U.S. officials were monitoring the situation closely.

Wirth called on the United Nations leadership, especially Secretary-General Boutros Boutros Ghali, to take a firm stand with the Chinese government about its obligations, as conference host, to refrain from intrusive security. Boutros Ghali has cancelled his visit due to illness.

"It's very important that we have the U.N. at the highest levels weighing in very firmly with the Chinese, very firmly with the authorities here, as to what the expectations are and are not. That is a responsibility that he (Boutros-Ghali) has," Wirth said.

"We are going to be in a situation where the United Nations is going to have to step up and be very, very firm with the host country and with the commitments that they have," he said.

Wirth called on Beijing to be a gracious host rather than alienating participants.

"The Chinese have here an enormous opportunity to show the world what they can do and how they can organize and I think they are incurring an awful lot of frustration and wrath from people in the way they are handling this," he said.

Wirth said that with mounting calls for reform at the United Nations, seen by many as bureaucratic and wasteful, the world body was at a crucial juncture.

"The United Nations ... has to demonstrate here that they can be firm and pull this off," he said.

Wirth said it was an established practice that U.N. rules and regulations, not those of the host country, prevail in the sites of U.N. conferences. China's security measures inside the venues were troubling, he said.

"You can have a demonstration there and do what you want to do," he said. "If you step outside that, you are a guest of the host country."

On the conference site, pairs of armed police with guns patrol the streets and police are deployed in large numbers.

"The governments are going to be reacting to this and, I think, reacting very strongly," the official said.

Chinese Vice Minister of Public Security Tian Qiyu said Monday that demonstrations at the NGO forum would be allowed only in a designated area and China would not tolerate slander or attacks on its leaders.

U.N. officials say China has no right to order or enforce such restrictions inside the forum and conference venues.