General Motors Corp. (GMGMQ) on Wednesday said it will shutter assembly and stamping Shreveport, La., factories by 2012, a move that came as concerns surfaced over what will become of unprofitable assets and liabilities being offloaded by the company.

GM builds small pickup trucks and some Hummer models at the plants. Sales of the trucks have fallen sharply, while GM early this month announced plans sell the Hummer line to a Chinese manufacturer. The plants join a list of nine others the auto maker plans to permanently close.

GMis expected to make public a list of which assets will go to "old GM" under the company's proposed bankruptcy sale by next week. Not all idled factories will go to the old company, as some sit on valuable land and could make money for the company.

Also Wednesday, a committee representing GM's unsecured creditors asked the court to require GM to make some changes to the sale proposal, citing concerns over what will become of the discarded assets and liabilities. Despite the worries, the group said it is satisfied that there are no viable alternatives to restructure the ailing auto maker other than the company's proposed bankruptcy sale.

The committee wants GM to permit lawsuits stemming from the activities of the "old GM" to be filed against the "new GM" after the sale closes. GM has said those lawsuits would have to be filed against the old company, which will have limited assets and resources to cover judgments from the suits. GM's bankruptcy plans, called a 363 sale, separate the company's more attractive assets, such as strong brands, from bad assets that are dragging the company down. Bad assets will be wound down in a lengthy liquidation.

The "new GM" assets would transfer to an entity owned by the U.S. and Canadian governments, the United Auto Workers union and the company's unsecured creditors. The company is hoping to emerge from Chapter 11 in mid-July, sooner than earlier projected.

As part of the plan, the company is looking to clear out between 10,000 and 16,000 hourly workers with retirement incentives and buyouts by Aug. 1, people familiar with the plans said. GM ultimately hopes to cut an additional 14,000 factory jobs by 2010, bringing the total hourly employment to 40,000. Local union leaders have told workers GM has set a cap of 16,000 takers for the offer, though the actual rate will likely be far lower as many workers have already left through previous retirement programs.

Meantime, Chrysler Group LLC said Wednesday it will permanently close its St. Louis North assembly plant effective July 10. The auto maker had planned to shut the plant in the third quarter but pulled ahead the decision due to dropping demand. Production of the Dodge Ram pickup will be moved, as planned, to a Warren, Mich., assembly plant.

-By Sharon Terlep and Marie Beaudette, Dow Jones Newswires; 248-204-5532; sharon.terlep@dowjones.com.