DETROIT (Dow Jones) -- General Motors Corp. (GM) for months has maintained it could hang on to U.S. market share despite moves to ax brands and nameplates.

But the auto maker on Monday conceded its likely to lose ground in its key market as it undertakes a new round of deeper cuts. New projections call for an 18.4% market share by 2012, down from the 20% GM projected in February.

Under the new plan, GM lowered its break-even point in the U.S. to 10 million car and truck sales. The company's previous plan would have required the U.S. market to reach 11.5 million before GM would stop losing money. The annual sales rate in March was 9.9 million vehicle sales.

GM has faced criticism on Wall Street for overly rosy projections for the U.S. market and the company's ability to perform. Just six months ago, GM was planning for a U.S. market of 12 million car and truck sales.

The projections were a key point of debate between the auto maker and U.S. Treasury, with GM arguing the depressed market has been tracking where the company anticipated.

The auto maker on Monday rolled out a more aggressive restructuring plan that calls for further job cuts, an additional plant closing and the elimination of Pontiac, along with the previously announced elimination of the Saab, Hummer and Saturn brands.

GM Chief Executive Officer Fritz Henderson said market losses will be driven largely by the auto maker's move to shed half of its eight brands.

The downsizing should allow GM to maximize capacity at its remaining factories. To be profitable, an auto plant typically needs to use at least 80% of its capacity. GM's factories will run around 50% capacity this year, then reach 120% utilization by 2012, under the new plan.

GM also sees its hourly labor costs shrinking to $4.1 billion by 2014, from $7.6B In 2008.

-By Sharon Terlep; 248-204-5532; sharon.terlep@dowjones.com.