Wal-Mart Stores Inc is considering bids from retirement plan managers to run its $15.6 billion 401(k) program, which has been administered by Bank of America's Merrill Lynch unit for 15 years, according to three sources familiar with the situation. The Bentonville, Arkansas-based retailer is talking to Wells Fargo & Co's retirement division about managing the program, the largest U.S. private sector plan, said the sources, who wished to remain anonymous because they are not permitted to speak to the media. Bank of America is also in the running, they said. It was unclear if other plan providers were also being considered. Wells Fargo, the No. 4 U.S. bank by assets; Bank of America, the No. 2 U.S. bank; and Wal-Mart declined to comment. While Wal-Mart accounts are much smaller than the average retirement account, the sheer size of the company makes it a coveted - and closely watched - client in the retirement industry. It could not be learned when Wal-Mart last conduc