MARCY GORDONWASHINGTON (AP) ¿ The federal seizure of struggling Florida thrift BankUnited FSB is expected to cost the Federal Deposit Insurance Corp. $4.9 billion, representing the second-largest hit to the FDIC's insurance fund since the financial crisis began felling banks last year. The costliest was last year's seizure of California lender IndyMac Bank, on which the bank insurance fund is estimated to have lost $10.7 billion. The Office of Thrift Supervision, a Treasury Department agency, said Thursday that BankUnited FSB reported $1.2 billion in losses last year as defaults on loans piled up. The thrift "was critically undercapitalized and in an unsafe condition to conduct business," the agency said in a statement. Coral Gables, Fla.-based BankUnited FSB is the 34th federally insured institution to be closed this year, and the biggest. Florida's largest banking institution with about $13 billion in assets as of May 2 was sold for $900 million to an investor group led by former North Fork Bancorp Chairman and CEO John Kanas. It will reopen as a newly chartered savings bank called BankUnited on Friday, with Kanas at the helm. The investor group includes several prominent firms: the Blackstone Group, the Carlyle Group, Centerbridge Partners and WL Ross & Co., the private-equity firm run by billionaire investor Wilbur Ross.