BEIJING (Reuters) - More than 180 Chinese dissidents and rights activists have signed a letter urging the International Olympic Committee to press China to improve its human rights record ahead of the 2008 Beijing Summer Games.

The open letter to IOC President Jacques Rogge, circulated on the Internet, said the human rights situation in China had worsened in past months with a series of jailings of reporters, rights activists and lawyers.

"Less than two years to go before the Olympics ... the Chinese government needs to mute critical voices in advance," the letter said. "That's the very reason they have been suppressing grassroots rights-defending movements on such a full scale."

The letter was signed by veteran Chinese dissidents such as Wei Jingsheng and Wang Dan, who are in exile in the United States, and advocates within China, such as Hu Jia and Zhao Xin.

They said they were not opposed to the Beijing Games altogether.

"But the 'harmony' of the Games should not come at the cost of Chinese people being deprived of human rights and the silencing of China's human rights cause," the letter said.

Beijing pledged during its bid that allowing it to host the Games would help advance human rights in China, but watchdog Amnesty International said last month that was not happening. China has dismissed the allegation as groundless, but analysts say the past year has seen a concerted crackdown on dissidents and activists, as well as on the media and Internet, shadowing its preparations for the Games.

A Chinese court jailed blind activist Chen Guangcheng for more than four years in August on charges that critics said had been trumped up by local officials angry at Chen for exposing arbitrary birth control measures such as late-term abortions.

Last week, police in the southern province of Guangdong formally arrested Guo Feixiong, a combative human rights lawyer, for "illegal business activities." Another prominent lawyer, Gao Zhisheng, was detained in Shandong province in August.

The open letter called on the IOC to press the Chinese government to free the three and "all other political prisoners, prisoners of conscience and religious prisoners," urging the IOC to draw lessons from the Nazi-controlled Berlin Olympics in 1936. It also drew parallels with the IOC's ban on white-ruled South African participation in the Olympics over apartheid. "We hope IOC could pay close attention to China's human rights as it did to South Africa's in the past," the letter said.

Responding to a similar appeal from Amnesty International last month, the IOC said it was not its place to pressure governments and it was premature to say China had failed to live up to the promises two years before the Beijing Games.