* World stocks lower as China surprises with tightening
* Wall Street set for losses
* Dollar gets boost
* Greek auction shows investor concern
By Jeremy Gaunt, European Investment Correspondent
LONDON, Jan 12 (Reuters) - World stocks fell on Tuesday and Wall Street looked set for a poor start as investors digested early results from the U.S. and European earnings seasons and reacted to a surprise monetary policy tightening in China.
The dollar rose on the China move with the Australian dollar the biggest loser given its trade links and the economy's regional exposure.
China's central bank said it was raising banks' reserve requirements by 0.5 percentage points, the first time it has adjusted requirements since it lowered the ratio in December 2008 as part of a loosening cycle.
It comes after signs that Chinese growth is again growing rapidly.
"This is a very pro-active measure to control inflation in China. Money growth rate is very fast and the output gap is closing," said Li-Gang Liu, head of China economics at ANZ Bank in Hong Kong.
MSCI's all country world stock index <.MIWD00000PUS> was down half a percent and Europe's FTSEurofirst 300 <
> lost 1.1 percent.Earlier, however, Japan's Nikkei <
> hit a new 15-month closing high, buoyed by China reporting record imports of some commodities and stronger-than-expected exports.Apart from China, earnings season was a key focus for many investors. U.S. aluminium producer Alcoa Inc <AA.N>, the first Dow Jones industrial average <
> component to announce results, reported earnings below Wall Street estimates after the closing bell on Monday."Many are now worried that the early miss by Alcoa could be the theme of what is likely to be a fairly mixed and crucial earnings season," said James Hughes, market analyst at CMC Markets.
Underlining the potential for a mixed picture, the world's fourth largest retailer, Tesco <TSCO.L>, smashed Christmas sales growth forecasts in its main British market.
GREECE WORRY
Elsewhere, market worries about Greece, reeling from a huge debt burden and downgrade, were on display with widening spreads while an otherwise successful T-bill auction commanded less buying interest and higher yields than previously. Greece successfully sold 1.6 billion euro in 6- and 12-month T-bills, but the auction produced a yield of 2.20 percent for the 52-week paper, up from 0.91 percent in a previous Oct 13 auction and higher than dealers had expected.
The bid-cover ratio was 3.05 versus 4.44, suggesting continuing, but weaker, demand.
Such auctions are usually dominated by domestic investors.
The dollar gained on China's move and had earlier been boosted by comments from Peng Junming, an official at China's $300 billion sovereign wealth fund CIC, that the currency had hit bottom and had limited room to fall further, while the yen would continue to weaken.
The dollar was up 0.2 percent against a basket of currencies <.DXY> and rose against the euro <EUR=>, but was a third of a percent lower against the yen. (Additional reporting by Simon Falush; editing by Stephen Nisbet)