By Jeff Mason DUJIANGYAN, China, Aug 21 (Reuters) - U.S. Vice President Joe Biden prodded China to expand citizens' rights on Sunday, but the tight security accompanying his visit to the nation's southwest showed the ruling Communist Party's determination to stamp out dissent. Biden used a speech at a university in Sichuan province to make a broad case for expanded human rights in China, where the ruling party pursued a crackdown on any form of opposition in the first half of 2012, fearing uprisings in Arab countries against autocratic rulers could inspire unrest at home. "I recognize that many of you in this auditorium see our advocacy of human rights as, at best, an intrusion and, at worst, an assault on your sovereignty," Biden said, in a nod to Chinese nationalist sentiment that can become riled by criticism from Western leaders. "I know that some in China believe that greater freedom could threaten economic progress by undermining social stability," Biden said in Chengdu, the provincial capital of Sichuan. "I believe history has shown the opposite to be true: that in the long run, greater openness is a source of stability and a sign of strength." But petitioners and would-be protesters in Chengdu, whom officials feared could try to approach Biden, were detained or warned to stay inside their homes, said Huang Qi, a veteran dissident in Chengdu who was released from jail in June after serving a three-year prison term for his activism. EARTHQUAKE SCHOOLS Since his release, Huang has resumed organising a group called "Tianwang" ( which campaigns to free detained dissidents, petitioners and rights advocates. "I'm relatively well-known by the international community, so local authorities have not made moves against me. But our Tianwang volunteers and many petitioners have been detained by the authorities," Huang said in a telephone interview. Huang said he knew about 10 petitioners and advocates associated with Tianwang who were detained before Biden's visit. The U.S. vice president also visited a school close to Dujiangyan, a small city near Chengdu badly damaged in the May 12, 2008, earthquake that devastated parts of Sichuan. At a high school there, Biden and Chinese Vice President Xi Jinping met a class of students studying English and took questions and as they sat casually dressed without ties or jackets. "I apologize that I don't speak Chinese," Biden told the students, who were quick to reassure him not to worry. With his counterpart sitting beside him, Biden did not mention human rights, but he did refer to "growing pains" in the U.S.-China relationship. According to a translator, Xi told the students the earthquake had made them more aware than people who do not experience disasters. The quake left 87,000 people dead or missing, most likely dead, including thousands of children who were killed when school buildings collapsed on them. Since the quake, aggrieved parents who lost children, and their supporters, have claimed that many of the schools were poorly built, because of corruption and lax standards. Sichuan officials said in 2009 the number of school children killed or missing from the earthquake 5,335, but critics say more died and the government failed to punish officials responsible for shoddy buildings disproportionately vulnerable to the quake. Some campaigners over the issue, including Huang, have been jailed. And the prominent artist-activist Ai Weiwei, whose detention early this year sparked an international uproar, also organised a campaign to document the children who died. But Biden was kept well away from such bitter memories, said Huang. The Qingchengshan High School he visited did not record any deaths during the 2008 earthquake. "Dujiangyan is also a sensitive area. There are petitioners complaining about losing children on May 12 or other complaints," said Huang. "But the authorities always have their own well-honed ways of making sure that they're in control. Biden won't see any of that." (Additional reporting by Chris Buckley in Beijing, editing by Miral Fahmy)