BEIJING -- With the rallying cry that "a revolution has begun,'' delegates Monday opened a global conference on women that was overshadowed before its start by complaints about heavy-handed Chinese policing.


Subjects that might discomfit the Beijing government surfaced almost immediately: At the opening session, Pakistani Prime Minister Benazir Bhutto condemned female infanticide. She did not single out China, but the practice is widespread here.


"The cries of the girl child reach out to us,'' Bhutto told delegates to the Fourth World Women's Conference. "This conference needs to create a climate where a girl child is as welcome and valued as a boy child.''


Over the next 12 days, the 3,000 delegates were to debate a proposed 120-page platform -- which conference secretary general Gertrude Mongella called a crucial social agenda -- urging steps to help women overcome poverty and win better health care, job opportunities and education.


China's Chen Muhua, elected conference president at the opening session, told the gathering that improving the lot of women "is not only a cry from the women's population, but a demand from the times.''


Mongella, meanwhile, won cheers and applause when she told delegates and Chinese dignitaries at a welcoming ceremony earlier Monday that women are no longer "guests on this planet.''


"This planet belongs to them, too,'' she said. "A revolution has begun, there's no going back.''


The latest confrontation with Chinese security came only hours before the formal opening of the conference, when Winnie Mandela was turned away from a Chinese welcoming ceremony after arriving late.


Chinese security men used coats to try to block cameras' view of their altercation with Mandela, estranged wife of South African President Nelson Mandela, and her bodyguards.


Chinese authorities have closely watched and occasionally harassed participants at the private forum that began last Wednesday in Huairou, a village outside Beijing. Tibetan exiles seeking independence for the Chinese-ruled Himalayan region have been particular targets.


By Monday, though, there were signs of a change in the Chinese attitude.


"We think there has been some relaxation and perhaps along the way some better understanding by the Chinese authorities about how UN conferences work,'' said Timothy Wirth, the U.S. undersecretary of state for global affairs. Illustrating that, guards at the Huairou site stood by quietly Monday while peace activists staged the largest demonstration yet at the private forum.


About 1,000 members of the group Women in Black stood for an hour in silence, holding placards protesting war, violence and poverty, then lit candles and marched for about a quarter of a mile. They did not attempt to leave the forum site.


The hands-off Chinese approach might be tested, however, by the visit of U.S. first lady Hillary Rodham Clinton, who is to address the official conference Tuesday and the unofficial meeting in Huairou on Wednesday. Some private activists hint they may try to stage protests, capitalizing on the attention generated by the visit.