Detroit - General Motors Corp is offering early retirement incentives to about 28 percent of its U.S. salaried work force as part of its effort to reduce payroll expenses and conserve cash.

The incentives were offered to about 9,000 U.S. employees, a person familiar with the plan said on Friday.

A GM spokesman confirmed the offers but declined to specify the target for buyouts or the details of the incentive offers.

GM's U.S. operation employs 32,000 salaried staff. The employees who have been offered early retirement have 45 days to consider the package, the person said.

The No.1 U.S. automaker said in July it would cut white-collar costs by 20 percent as part of its effort to reduce overall costs by $10 billion and shore up cash.

GM, which has lost $51 billion over the past three years as it has cut jobs and closed plants, has been under intensifying pressure to cut costs and raise capital because of the slump in U.S. auto sales that pushed its first-half sales down 16 percent.

High fuel prices, a consumer shift away from low-mileage trucks, the weakest U.S. auto sales in a decade have increased investor doubts about the automaker's ability to ride out the downturn.