NEW YORK, June 8 (Reuters) - Private equity firm Thomas H. Lee Partners has filed to raise up to $300 million and take its credit unit public as a business development company in a blind pool IPO, according to a regulatory filing.

THL Credit anticipates its portfolio will be primarily comprised of investments in mezzanine loans made to middle-market companies, according to a filing last week with the U.S. Securities and Exchange Commission.

In a blind pool or "blank check" initial public offering, money is raised with few restrictions from investors based on the reputation of a particular individual or firm.

The filing did not give an indication of the timing of the IPO.

THL Credit will be led by James Hunt, the former chief executive of Bison Capital, and Sam Tillinghast, the former head of American International Group's (AIG.N: Quote, Profile, Research) private placement group.

"Because the general economic climate and financial markets have deteriorated since the summer of 2007, we believe opportunities to invest in solid, underserved middle-market companies remain plentiful," THL Credit said in the filing.

The deal's underwriters are Bank of America's (BAC.N: Quote, Profile, Research) Merrill Lynch & Co, Citi (C.N: Quote, Profile, Research) and Deutsche Bank Securities (DBKGn.DE: Quote, Profile, Research).

THL Credit has applied to list on the NASDAQ Global Select Market under the symbol "TCRD." (Reporting by Phil Wahba, editing by Leslie Gevirtz)