The conference is the third worldwide gathering since a committee led by the evangelist Billy Graham drew 2,700 religious leaders to Lausanne, Switzerland, in 1974. Organizers say most of the speakers are from Africa, South America and Asia because that is where two-thirds of evangelicals live today.

Beginning in July, Chinese officials began individually contacting every Chinese citizen who had been invited and pressuring them not to attend, church leaders said. Some had to give up their passports, some suffered government reprisals against their churches and some were detained, the letter said. Most were turned away at airport passport control checkpoints, according to the letter. “This series of blocking actions violated their right of religious freedom” spelled out in the Chinese Constitution, it stated.

There is precedence for the government’s interference. In accordance with China’s policy against foreign oversight of religion, the Chinese Patriotic Catholic Association, which officially represents Chinese Catholics, does not recognize the authority of the pope. Ignoring that, Pope Benedict XVI invited four Chinese bishops to attend a church conference in Rome in 2005. Government authorities rejected the invitation.

Mr. Liu, the Beijing evangelical leader, said a half-dozen police officers and government officials met him and four other Christians at the Beijing airport about an hour before their Sunday flight was scheduled to board. He said that his passport was confiscated and that he was ordered not to speak to the foreign media. A 25-year-old Beijing education worker, who asked to be identified only by his English first name of David in order not to call attention to his church, was sent home along with Mr. Liu. He said he later demanded a written explanation of why his passport was seized. The letter he received was brief, he said. It stated that he had volunteered to give his passport to the police.

Demanding Release of Dissident

BEIJING  More than 100 Chinese intellectuals and dissidents signed and posted a letter online Friday, asking that the Nobel Peace Prize winner, Liu Xiaobo, be released from prison and that government security officers stop harassing his wife, Liu Xia. The signers also asked that government leaders “make good on their oft-repeated promise to reform the political system,” in line with Charter 08, the pro-democracy manifesto of which Mr. Liu was a writer and that led to his imprisonment.

The letter added, “This will require it to guarantee the rights of Chinese citizens as they work to bring about peaceful transition toward a society that will be, in fact and not just in name, a democracy and a nation of laws.”

A leading dissident and supporter of Mr. Liu, Ding Zilin, meanwhile, was reported to have vanished, last heard from in the Yangtze River Delta town of Wuxi on Oct. 8, days after Mr. Liu’s prize was announced.