China's Communist rulers gather next week for a key meeting devoted to the "rule of law", but observers say the conclave will in fact mark another tightening of control by party leader Xi Jinping after crackdowns on internal dissent and graft.

The Fourth Plenum brings together the party's 205-strong Central Committee and around 170 reserve members, along with officials from bodies including its much-feared internal watchdog, the Central Commission for Discipline Inspection.

The gathering, typically held at a Beijing hotel, is expected to take action against Zhou Yongkang, the powerful former domestic security tsar who fell to the anti-corruption campaign Xi launched with much fanfare after coming to power two years ago.

At the same time, China has seen a broad crackdown on dissent, and the meeting comes as authorities arrest an increasing number of lawyers.

The Politburo announced in July that the plenum will focus on "governing the country according to the law" to ensure "economic growth, clean government, social justice", the official Xinhua news agency reported.

But the concept is seen very differently in Beijing than in the West, analysts say.

In a commentary this week the state-run Global Times newspaper assured readers that rule of law will not challenge the "people's democratic dictatorship".

"For the party, 'rule of law' means what we would call 'rule by law': using the legal institutions -- procurators, courts, lawyers -- to continue to enforce one-party rule," said Andrew Nathan, a China scholar at New York's Columbia University.

Xi is using the concept as part of a "recentralisation of power" under him, he added, with reforms intended to make the state "even more functional and efficient" at authoritarian rule.

- 'Picking quarrels' -

The campaign against dissent has seen dozens detained, many for the nebulous crime of "picking quarrels and provoking troubles", and targeted even moderate critics of the Communist Party, including rights lawyers Xu Zhiyong and Pu Zhiqiang, to activists' alarm.

New York University professor Jerome Cohen said the arrests showed Xi believes control through the legal system "requires repression of any voice that might oppose any of his views".

"Han Feizi and Shang Yang, the great ancient Legalist advocates of dictatorship in China's history, took a similar view," said Cohen, citing two Chinese statesmen Xi has quoted in recent months from the Warring States period of the fifth to third centuries BC.

More recently, Cohen added, "At the height of his infamous public purges in 1937, Stalin said: 'We need the stability of the laws more than ever'."

Ironically, many of the detained advocates had been defending citizens exercising rights enshrined in China's own constitution, said University of Hong Kong law professor Michael Davis.

"Those lawyers are upholding the rule of law because they're trying to represent their clients who are resisting property seizures, exercising free speech on the Internet or religion," he said.

Party leaders have also suggested pursuing greater "judicial independence" at the plenum, although experts warn that similarly the phrase is not what it appears.

Chinese courts are tightly controlled by the party and have a near-100 percent conviction rate in criminal cases.

Authorities are looking to have local courts controlled by higher judicial bodies rather than local governments, the Global Times reported Friday -- which would allow Beijing greater control.

Xi "does not mean the local courts should be independent of the central party", said Cohen.

- Anti-corruption campaign -

Xi has repeatedly promised to target both low-level "flies" and high-level "tigers" in the anti-corruption drive and so far 51 officials of vice-ministerial rank and above have been dismissed, according to an AFP tally.

The highest-ranking is Zhou Yongkang, who rose through the oil sector to the elite Politburo Standing Committee, the party's innermost circle.

He is the most senior official to be investigated for decades, and his long-rumoured fall sent an unmistakable signal of Xi's authority through the factionalised party.

According to the website of the Communist Party mouthpiece People's Daily this week, the plenum is likely to announce whether Zhou and his allies will be expelled from the organisation and sent for trial.

Jeffrey Wasserstrom, a China expert at the University of California Irvine, said that while the anti-graft drive has had an impact, "we know that there is some corruption close to the families of people in very high positions close to Xi".

"If those people are still immune, there's a question about how big a jump it is from what we've seen before," he said of the campaign. "This one is quantitatively different, it's just not qualitatively different."