* Investor group includes WL Ross, Carlyle, Blackstone

* BankUnited had $12.8 bln in assets, largest Florida bank

* Was 34th U.S. bank to fail so far this year (Adds details on BankUnited, FDIC guidelines on investments)

WASHINGTON, May 21 (Reuters) - U.S. bank regulators on Thursday closed troubled lender BankUnited Financial Corp BKUNA.O, Florida's largest bank, and sold its banking operations to a private equity consortium that includes WL Ross & Co.

BankUnited, which had $12.8 billion in assets and $8.6 billion in retail deposits, is the biggest of 34 U.S. banks to fail so far this year.

The Federal Deposit Insurance Corp said it estimates BankUnited's failure will cost its insurance fund $4.9 billion.

The private equity group buying BankUnited is headed by John Kanas, a veteran of the banking industry and former head of North Fork Bank. Other members of the group, besides WL Ross & Co, include Carlyle Investment Management [CYL.UL], Blackstone Capital Partners (BX.N: Quote, Profile, Research), and Centerbridge Capital Partners.

BankUnited's 86 offices will open on Friday during normal business hours, the FDIC said.

Bank failures have accelerated in 2009, mainly due to soured real estate loans. The 34 bank seizures so far compare to 25 in 2008 and just 3 in 2007.