Bethesda-based Lockheed Mar­­tin said Wednesday that about 340 employees will leave the defense contractor as a result of a buyout program offered to about 6,500 employees in July.

About 190 employees volunteered to take the buyout, which offered a special severance package to all U.S.-based, salaried employees who report to Lockheed’s corporate headquarters or an internal business services organization that handles areas such as payroll and information technology for the company.

Lockheed also has laid off an additional 150 workers in its internal business services unit, a step that that company spokesman Rob Fuller said in a statement was “necessary to improve the affordability of our business and increase operational efficiency.”

Although the company said that about 2,000 of the eligible employees are based in the D.C. area, Fuller declined to identify how many of the departing employees work in local offices.

The internal services unit employs about 5,000 people overall, not all of whom were eligible for the buyouts. Many are based in Florida — at Orlando and Lakeland offices — or in Denver and Fort Worth.

The severance package provides two weeks of pay, plus another week of pay per year of service, up to 26 weeks.

The layoffs come as defense contractors continue to struggle with anticipated Pentagon cuts. McLean-based Science Applications International Corp., for example, last week reported sales and profit declines and said it would reduce its financial forecasts for the year.

Lockheed, the world’s largest defense contractor, has been aggressively trimming its staff for more than a year. Last summer, it bought out about 600 top executives. More recently, it has announced layoffs in its aeronautics and space systems businesses.