By Megan Davies and Phil Wahba

NEW YORK (Reuters) - Discount retailer Dollar General Corp, backed by powerful private equity firm Kohlberg Kravis Roberts & Co <KKR.UL>, filed for an initial public offering of up to $750 million on Thursday, according to a regulatory filing.

It could be one of the largest IPOs of the year and among the biggest exits through a public stock offering by a private equity firm since the credit crunch sapped investor appetite for new offerings.

The IPO market has been improving since the spring, as stock markets have rallied.

The lead bookrunners will be Citi <C.N>, Goldman Sachs & Co <GS.N>, Bank of America Merrill Lynch <BAC.N>, J.P. Morgan <JPM.N>, as well as KKR itself.

The company said it expected to pay a special dividend of $200 million to existing shareholders prior to the offering.

An IPO of the retailer had been expected. A source familiar with the situation previously told Reuters that advanced preparations were in place to take the Tennessee-based company public, which could happen in the late third quarter or fourth quarter.

Dollar General did not specify timing of the IPO in the filing.

A successful IPO is particularly important for KKR, which is itself looking to join rival Blackstone Group <BX.N> in becoming a publicly traded company through a complex transaction that involves combining with its Amsterdam-listed fund KKR Private Equity Investors <KKR.AS> (KPE).

KPE earlier this week said it marked the value of its investment in discount retailer Dollar General $116.2 million higher for the three months to June 30.

Dollar General did not specify how much it expects the IPO to yield but said it planned to use the proceeds to pay down debts and notes.

(Reporting by Megan Davies and Phil Wahba, editing by Matthew Lewis)