UPDATE 1-GM files for landmark IPO to repay bailout

* GM files for IPO worth up to $100 million

* U.S. Treasury expected to shift to minority GM stake

* IPO follows CEO shake-up, biggest profit in six years

* Morgan Stanley, JPMorgan, BofA, Citi lead underwriters

NEW YORK/DETROIT, Aug 18 (Reuters) - General Motors Co [GM.UL] filed for an initial public offering of stock on Wednesday, clearing a key hurdle toward repaying taxpayers for a controversial bailout just over a year after its bankruptcy.

Morgan Stanley (MS.N), JPMorgan (JPM.N), Bank of America Merrill Lynch (BAC.N) and Citigroup Inc (C.N) have been selected as the lead underwriters for the IPO by the top U.S. automaker.

GM's initial filing with U.S. securities regulators did not say how many shares would be sold or give an expected price range for what will likely be one of the biggest IPOs ever.

GM filed for an IPO of up to $100 million. That does not represent the full amount that GM hopes to raise, people familiar with the situation have told Reuters. GM could raise up to $20 billion in its IPO, the people said.

The automaker said it planned to list the shares on the New York Stock Exchange and the Toronto Stock Exchange.

Trading in GM shares is expected to start between late October and the U.S. Thanksgiving holiday, which is the fourth Thursday in November, according to people involved in the process. A stock offering in late October would mean trading would start just before the November congressional elections.

The Obama administration wants to be able to cast the $50 billion GM bailout as a financial success in the face of public skepticism and Republican political opposition. (Reporting by Clare Baldwin in New York and David Bailey and Kevin Krolicki in Detroit, editing by Matthew Lewis)