SEOUL (Reuters) - South Korea's top regulator said Sunday it would receive preliminary bids for a 6 trillion won ($5.28 billion) controlling stake in Woori Finance Holdings (>> Woori Finance Holdings Co., Ltd.) by July 27, after two previous attempts to privatize the group floundered over a lack of bidding interest.

Authorities are under pressure to dispose of the stake before the current president, Lee Myung-bak, ends his term in office early next year. They face an uphill struggle with few domestic firms boasting the capacity for the deal and U.S. fund Lone Star's years-long struggle to offload a stake in Korea Exchange Bank (>> Korea Exchange Bank) still fresh in foreign investors' minds.

"We plan to pick a preferred bidder around early October," Kim Yong-beom, a senior official at the Financial Services Commission (FSC), told reporters.

A sale notice for the stake will be put up on April 30.

Kim told a briefing that it was open to every option, including a merger with a local financial holding company.

The government, which owns 57 percent of Woori, has done little to change the sale framework, but there are more favorable circumstances for investors following a revised law that allows bidders to buy new shares of a merged company, the FSC said.

It's unclear which potential bidders may emerge. KB Financial Group Inc. (>> KB Financial Group Inc), seen by some analysts as the most likely local suitor, has said it lacks the financial capacity for the acquisition.

Kim Seok-dong, chairman of FSC, said earlier that the government had to fulfill the privatization project before presidential elections in December.

The sale of Woori is the lynchpin of President Lee Myung-drive to reduce state ownership and recoup billions of dollars of taxpayers' money spent to rescue the financial sector in the wake of the Asian financial crisis in the late 1990s.

JP Morgan (>> JPMorgan Chase & Co.), Samsung Securities (>> Samsung Securities Co., Ltd.) and Daewoo Securities (>> Daewoo Securities Co., Ltd.) are managing the deal, as they did previously. ($1 = 1136.3000 Korean won)

(Reporting by Ju-min Park; Additional reporting by Se Young Lee; Editing by Jonathan Hopfner)