By Summer Zhen and Xie Yu

HONG KONG, Sept 28 (Reuters) - Investors are dialling back risk exposure ahead of China's Communist Party Congress in October and sticking money in the relative safety of mainland blue chips as they await signs Beijing is ready to address problems hanging over the economy.

The ChinaAMC China 50 ETF, the country's largest exchange-traded fund, has witnessed a near 30% jump in its assets this month, channelling more than 10 billion yuan ($1.40 billion) into Shanghai's 50 biggest stocks.

That's driven by what some analysts term the "Beijing put", the belief that authorities will keep markets stable ahead of the 20th Communist Party Congress, to be held from Oct. 16.

But investors have little appetite to make bets about what happens beyond that event, which would see Xi Jinping anointed for a third five-year term as the supreme leader and a shuffle of personnel on the decision-making Politburo.

It's a challenging time for the economy as authorities prioritise political stability over growth, the yuan slides and global equity markets sell off.

Investor positioning is markedly conservative, with most betting on A-shares, seen as more resilient and as having the lowest correlation with U.S. and European markets

They also hope issues currently clouding investor confidence, such as zero-COVID policies and property sector stress, ease after Xi's reappointment.

"We are quite defensive and cautious on China this year, still underweight China, but what we are monitoring are more of the positive signposts that are coming through," said Robert St Clair, a strategist at Fullerton Fund Management in Singapore.

St Clair says Fullerton likes A-shares as domestic-listed firms in new technologies and industries could benefit from the country's common prosperity initiative.

Francois Savary, chief investment officer at Prime Partners SA, a Swiss wealth manager with around $4.1 billion of assets, says it is difficult for investors to avoid China exposure.

Key questions centre on what happens after the Congress and whether Xi will take a reformist or conservative approach to economic management.

"Can the Congress change everything, and can it stabilise the situation in China?" Savary said. "I don't think so."

Staying neutral is a safe option while there is uncertainty about what a more powerful Xi would do, he said, given Beijing's recent push to clean up the real estate and tech sectors and his long-term desire for a more self-sufficient and equitable China.