Chinese exports leap, put yuan back under microscope

* Chinese exports beat expectations despite Europe worries

* China May exports up 48.5 pct yr/yr, imports up 48.3 pct

* Jump in exports, surplus hands ammunition to U.S. critics

* Chinese economists question if momentum can be sustained

China's exports jumped in May, reassuring investors about the economy's strength but putting pressure on U.S. President Barack Obama to placate critics who say Beijing is keeping the yuan unfairly undervalued.

Imports also grew robustly, testifying to the underlying momentum of the world's third-largest economy despite government steps to cool the red-hot property market.

Some economists said the export surge would be short-lived given debt problems in Europe, the country's biggest overseas market, but several said it would revive a debate about the timing of a long-awaited resumption in the appreciation of the Chinese currency. >>