CORRECTED-BHP voices doubts about global commodity rally

(Corrects RIC in first paragraph to (BLT.L))

* BHP Billiton CEO says global demand picture unclear

* China commodity-buying not entirely reflecting real demand

* Declines comment on iron ore pricing (Adds quotes, background, share price)

CANBERRA, May 27 (Reuters) - The head of BHP Billiton (BHP.AX) (BLT.L), the world's top miner, voiced doubts on Wednesday about the durability of recent strong Chinese demand for commodities and said the picture for global demand was unclear.

Signs of a strong pick-up in Chinese demand for industrial raw materials have fuelled a rally in commodity prices, with three-month copper surging more than 50 percent so far this year.

But BHP Chief Executive Marius Kloppers, in giving a cautious market outlook in a speech to a mining conference, pointed out that average commodity prices were still about 50 percent below their peaks, though he later declined to comment to reporters on recently renegotiated iron ore prices.

On Tuesday, rival global miner Rio Tinto Ltd (RIO.AX) (RIO.L) and Japanese steel mills agreed to cut key iron ore prices by a third in this year's first contract deal, setting a benchmark that China's embattled mills will almost certainly resist.

China reported record imports of iron ore for April, another sign for commodity-market bulls that the wider rally has firm foundations, but Kloppers said the global demand picture was still unclear and should take around six months to resolve.