NEW YORK (Reuters) - Maurice (Hank) Greenberg, the former chief executive of American International Group Inc , will testify tomorrow over a sham transaction involving the insurer and a unit of Warren Buffett's Berkshire Hathaway Inc, a judge ruled.

New York State Supreme Court Justice Charles Ramos ordered the deposition after Greenberg last week said he was ready to testify in a 2005 civil fraud lawsuit brought by then-New York Attorney General Eliot Spitzer, and now handled by his successor Andrew Cuomo.

The case involves a 2000 reinsurance transaction with Berkshire's General Re Corp unit that boosted AIG's loss reserves by $500 million without transferring risk. Former AIG chief financial officer Howard Smith also was charged in the New York lawsuit.

Federal prosecutors have obtained five convictions and two guilty pleas of former General Re and AIG officials over the transaction, including a conviction of onetime General Re chief executive Ronald Ferguson.