WASHINGTON - The Treasury Department will audit General Motors Co.'s initial public stock offering and estimates that the stock must sell for $133.78 a share for the government to break even.

Neil Barofsky, the Treasury's special inspector general, told Reuters news agency that he will watch over GM's IPO -- expected late this year -- and said, "I expect it will be a broad inquiry."

Barofsky, the government's watchdog over the $700 billion Wall Street and auto industry bailout, said that "it's important for us to do effective and quick audit work so we can learn the lessons from this IPO."

As a result of the bailout, the government holds 304.13 million shares of GM common stock. It also holds $2.1 billion in preferred stock in the Detroit automaker, but does not expect to sell that stake during the IPO.

GM plans to sell up to $3 billion in mandatory convertible preferred stock to raise more cash for operations.

The Detroit automaker hopes to mount a worldwide roadshow soon after the Nov. 2 midterm elections to convince investors to buy its stock.

Sen. Charles Grassley, R-Iowa, asked Barofsky in August to watch over the IPO to see that U.S. taxpayers get the "highest possible return" on their bailout investment.

He also asked the Treasury to investigate GM's planned $3.5 billion acquisition of Texas-based subprime lender AmeriCredit. The company's shareholders are to approve the tie-up Sept. 29.

The $133.78-per-share figure was disclosed in a two-page letter to Grassley that was obtained Wednesday by The Detroit News.

That would mean GM would have a market capitalization of around $70 billion. Some analysts have predicted that GM will be worth more than $100 per share.