Northrop Grumman, the Pentagon’s number three supplier, is cutting up to 750 jobs, mainly administrative positions in Southern California, even as it plans to hire up to 850 engineers and technicians for work on advanced weapons.

The layoffs stem chiefly from the consolidation of Northrop’s aircraft-making Integrated Systems unit, headquartered in El Segundo, with the satellite-building Space Technology unit, based in Redondo Beach.

Employees were informed this week of a voluntary departure program, that will precede up to 750 involuntary job losses.

Meanwhile, the new combined Aerospace Systems unit will hire up to 850 highly skilled workers.

Northrop Grumman is an aerospace and defense technology company formed by the 1994 purchase of Grumman by Northrop. The company is the fourth largest defense contractor in the world, and the largest builder of naval vessels. Northrop Grumman employs over 122,000 people worldwide.