General Motors plans to complete a one fifth cut in its white collar work force by October, a spokesman has said.

The plan, detailed in letters to employees sent on Tuesday, would eliminate another 4,000 jobs through a combination of layoffs and terminations.

"This is what we've talked about - a leaner organisation with fewer levels of management," GM's Tom Wilkinson told Reuters. "You start to see what the new organisation will look like."

GM has said it plans to cut 20% of its remaining white collar jobs as it sheds its Hummer, Saab and Saturn brands and slashes manufacturing capacity.

The automaker also plans to cut 35% of its more senior executive ranks, the report noted.

By the end of the process, GM plans to have 23,500 white-collar workers in the United States, down from over 49,000 in 2000 and about 29,600 at the start of the year.

GM salaried workers have until August to indicate if they are interested in taking severance of up to six months of pay, depending on their length of employment. Other job cuts would be made through firing, the report said.

The automaker has also slashed 60,500 US factory jobs since 2006, more than half of its blue collar work force. Workers represented by the United Auto Workers are also being offered another round of buyouts this month.