The call for volunteers to quit their jobs came in early October because the company wants to reduce infrastructure costs.
"This workforce reduction action is regrettable, but unavoidable, [and is] in response to economic uncertainties and defense budget cuts," the company said in a statement.
Northrop wants to complete the reduction by the end of the first quarter of 2013. If enough volunteers don't step forward, layoffs will follow.
In addition to this year's defense budget, the aerospace and defense sectors are facing $500 billion in automatic spending cuts over the next 10 years because the so-called congressional Super Committee failed to resolve budget issues last year. Those cuts start on Jan. 1, unless Congress and President Barack Obama reach a deficit-reduction agreement by Dec. 31.
Northrop is the second big aerospace company to announce cuts during the fourth quarter. On Nov. 8 California-based Pratt & Whitney Rocketdyne laid off 100 workers at facilities across the country.
Kimberly Ritter-Martinez, an economist at the Kyser Center for Economic Research in Los Angeles, said that the job cuts are not surprising given the economic and political environment.
"I think just about everybody has been hit by it," she said of job cuts. "If you look at a company like Northrop Grumman, about 90 percent of their sales come from the government. Any kind of budget cut is going to have a huge impact."