The U.S. Treasury is offering to sell $18 billion of American International Group Inc. shares in a transaction that is likely to cut taxpayers’ stake in the firm to below 50 percent for the first time since its 2008 bailout, Bloomberg News reported today. The insurer plans to buy back as much as $5 billion of the shares and Citigroup Inc., Deutsche Bank AG, Goldman Sachs Group Inc. and JPMorgan Chase & Co. are managing the sale, the Treasury said yesterday. The U.S. would own about 23 percent of AIG if it sells the shares at the Sept. 7 closing price of $33.99 each, data compiled by Bloomberg show. Treasury had cut its stake in the New York-based firm to 53 percent in four earlier share sales, which raised about $23.3 billion. The last offering, announced Aug. 3, came the same week that AIG reported a 27 percent increase in second-quarter net income to $2.33 billion, driven by improving results at its property-casualty operation.