BEIJING, Oct 10 (Reuters) - A well-known Chinese human rights campaigner has disappeared and is probably in secret detention, his son said on Wednesday, as the government imposes strict controls on dissidents ahead of a key Communist Party meeting.

Yao Lifa, from rural Hubei province in central China, is known for dogged campaigns to win an independent seat in his local Party-controlled congress and to organise citizens, especially disgruntled farmers, to challenge long-standing restrictions on political activity.

His son, Yao Yao, told Reuters that his father was apparently taken away on Oct. 1 as part of a sweep of potential protesters before the Communist Party convenes a five-yearly congress next week.

"I heard from a source with good information that he's been put in detention, probably until after the congress, but we haven't heard anything official," said Yao Yao, who is currently studying in New York.

A police officer in Yao Lifa's hometown, Qianjiang, said he did not know anything about his disappearance.

"I haven't heard about that," said the officer, surnamed Wang, when asked whether Yao may be in informal detention. "I know who he is but I don't have any information about this."

There seems no doubt, however, that wary authorities are taking extraordinary precautions against protests before the Congress, when President Hu Jintao is set to seal another five years as national leader.

The streets of Beijing have been awash with police and plainclothes guards, whose neat haircuts and wary stance mark them out.

They question and often take away passers-by whose ruddy features and rumpled clothes suggest they may be rural petitioners intending to air complaints about lost land, corruption and official abuses during the Congress.

Other dissidents were also reported being under house arrest ahead of the congress, among them Hua Huiqi, an outspoken leader of a Christian "house church" in Beijing who was only recently released from jail.

"Whenever there's a big meeting or event, the government keeps him under house arrest or tails him," said Hua's wife, Wei Junmei, who said by phone that she was also under informal detention with him.

Hu Jia, an activist whose campaigns embrace AIDS, political rights and Tibet, has been under house arrest since May but said the plainclothes guard around his apartment has been intensified since September.

"That shows how worried they are about anything at all that could upset plans," said Hu by phone.

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