* European shares hold clear of 2012 lows
* Euro edges up from two-year trough
* French benchmark bond yield at euro-era low
* Greek euro exit contagion fears dominate backdrop
By John Stonestreet
LONDON, May 25 (Reuters) - The potential fallout from a Greek exit from the euro zone and worries about the global economy weighed heavily on financial markets on Friday, snuffing out a tentative rally in stocks and setting up a mixed outlook for Wall Street's open.
U.S. stocks futures pointed to gains on the broad S&P 500 index but losses on the blue-chip Dow Jones industrial average.
A comment from Belgian Deputy Prime Minister and Foreign Minister Didier Reynders set the mood.
"If central banks and companies are not preparing for the scenario (of Greece leaving the euro zone), that would be a grave professional error," he told a conference in Paris.
The FTSEurofirst 300 index was down 0.2 percent at around 980, not too far from its May 21 trough of 952.55 points, its lowest point since December 20.
"Europe is in a recession, China is slowing down and the United States is slowing down as well," said Michel Juvet, chief investment officer at Swiss bank Bordier & Cie.
There was, nonetheless, some upbeat economic news. German consumer morale held steady going into June while Chinese exports showed signs of recovery in early May, countering dire recent data that suggested Europe's growth engine was no longer immune from the region's debt crisis and factory output in the world's number two economy was faltering.
The modest data boost helped keep the euro above two-year lows of 1.25155 as bearish investors took a breather from a sharp sell-off. But the common currency stayed on track for its fourth straight week of losses.
Safe-haven flows drove the index that measures the dollar against key currencies to a fresh 20-month peak.
"Markets have priced in a very negative scenario for Greece as well as deteriorating growth prospects in the euro zone, but with them very much focused on the tail risk of Greece leaving the euro bloc, the euro remains highly vulnerable," said Masafumi Yamamoto, chief FX strategist at Barclays.
With the euro zone mired in crisis, there was speculation that European policymakers might soon intervene,
Credit Agricole said the European Central Bank could announce new stimulus measures next month, such as another round of emergency funding for banks in the region.
"We expect the ECB to make a move (at its next rate-setting meeting) on June 6," it said in a research note.
ECB action then could help lift the prevailing mood of uncertainty among global investors who remain sharply focused on June 17 elections in Greece that will largely determine if Greece gives up the euro.
One opinion poll on Thursday showed the anti-bailout leftist party SYRIZA maintaining its lead ahead of the vote.
The unclear outcome of the ballot has also driven debt markets, sending yields on safe-haven German bonds to record lows and culminating on Wednesday in a sale of two-year Bunds that drew strong demand despite carrying an unprecedented zero coupon.
On Friday, a tentative search for higher returns prompted a sharp rally in non-German debt, with the yield on French 10-year bonds - viewed as a viable alternative to Bunds - falling to 2.5 percent.
Other euro zone sovereign yields also fell. The equivalent benchmark German yield was 1.38 percent.
"The (debt) market is trading political headlines which means, in turn, the market will remain very volatile for the time being," said DZ Bank strategist Michael Leister.
The underlying mood earlier saw Asian shares outside Japan post a third consecutive week of losses to hit their lowest levels of the year.