China will keep appropriate investment growth in 2012 to help underpin the economy amid the global downturn, the country's top economic planner said in comments published on Sunday.

The key to maintain steady and relatively fast economic growth is expanding domestic demand, the China News Service quoted Zhang Ping, the head of the National Development and Reform Commission (NDRC), as saying.

The government will maintain an appropriate level in investment next year while promoting further expansion in consumption, Zhang was quoted as saying.

The government will ensure the completion of state projects under construction while kicking off key projects under the 12th five-year plan (2011-2015) and spending more on cheap housing, education and water conservation, Zhang added.

Zhang reiterated plans to encourage private investment in railways, utilities as well as financial and energy sectors.

Zhang did not reveal targets on investment growth in 2012.

The government aims for an 18 percent annual rise in fixed-asset investment in 2011 and 16 percent increase in retail sales -- a key gauge of consumption.

Beijing has promised to do what it can to foster growth. It concluded its policy-setting conference on Wednesday with a vow to guarantee growth in the face of an extremely grim outlook for the world economy.

But Chinese officials have cautioned against unveiling fresh fiscal stimulus to boost investment given the hangover from its 4 trillion yuan ($629 billion) stimulus package unveiled in 2008, which has led to piles of local government debt.

Instead, they have pledged to support consumption by lifting household incomes and shoring up social safety nets.

(Reporting by Kevin Yao; Editing by Robert Birsel)