General Motors Corp. (GMGMQ) will cut 4,000 U.S. white-collar jobs by Oct. 1 as part of an accelerated plan to shrink its workforce.

The bankrupt auto maker plans to eliminate more than 6,000 salaried jobs by the end of the year, up from an earlier announced reduction of 3,400 workers.

The cuts will be made through a combination of layoffs and separation incentives, GM spokesman Tom Wilkinson said. Some workers can opt to either quit and receive six months of pay and benefits or to retire early with full benefits.

Workers on Tuesday received letters notifying them of their options.

The auto maker, which filed for Chapter 11 protection on June 1, has been downsizing for years. But the pace of everything from plant closures to job cuts accelerated dramatically earlier this year after the Obama administration rejected the company's restructuring plan.

GM Chief Executive Fritz Henderson warned that more salaried jobs will need to go.

The company said in February it would eliminate 10,000 of 73,000 salaried jobs around the world, with duties that include marketing, engineering and design.

The auto maker also is cutting executive ranks by 34%.

When all is done, GM will have 23,500 salaried workers in the U.S., just over half what it had in 2000.

GM also has eliminated tens of thousands of hourly jobs, as well as winning concessions and cutting pay and benefits from all workers.

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