Petitioners hold up documents listing their grievances near a petition office this week in Beijing. As the Olympics approach, the Chinese government is trying to suppress dissent that could be seen as unflattering to the country.

Beijing ? Lu Jun, a campaigner for the rights of millions of Chinese with hepatitis B, seems an unlikely threat to the Beijing Olympics.

But the popular Web site he runs was blocked in May. This month, police detained him for four hours when he returned to China from a hepatitis conference in Los Angeles. They wanted to know what he intended to do with a large red banner he was carrying that urged the government to provide support to people with hepatitis B.

“Everyone believes it’s because of the Olympics,” Lu said.

As Beijing enters the final stretch before the August 8-24 Olympics, the government is trying to shut out anyone it believes might mar an event meant to showcase China as a modern nation. AIDS activists have been followed by police and beggars rounded up.

This week, petitioners in from the provinces to request the government’s intervention in local squabbles were being rounded up by police, plainclothes officers or hired thugs, who sometimes packed them into waiting vans to be sent back home.

“Now I can’t stay in hotels. I have to live on the streets because if I ever register my name the police will kick me out,” said Wang Lijun, 37, nervously clutching copies of his complaint letters amid 40 or so petitioners Wednesday.

Wang has traveled countless times to Beijing, trying to recoup unpaid pension benefits for his father, a World War II and Korean War veteran later labeled a political criminal. But in recent months, Wang said, officials in his home in barren Shanxi province and in Beijing have twice told him not to travel to the capital because of the Olympics.

Beijing began tightening its already strong squeeze on political activists more than a year ago, and since then has targeted others regarded as potential troublemakers. In January, Beijing Communist Party Secretary Liu Qi, who also heads the Olympic organizing committee, was quoted in state media as saying beggars and vagrants would be cleared away for the games.