Eastern Airlines, which earlier reported a third-quarter net loss of $67 million, announced plans yesterday to lay off 3,500 workers -- or approximately 9 percent of its work force.

The Miami-based company, which has shed plenty of red ink over the years, said it anticipates further losses in the fourth quarter of this year. In addition to the layoffs, the company announced the sale of three DC-9-30s. The company has cut back capacity by 10 percent and has sold or leased 19 planes so far this year.

Phil Bakes, Eastern's president and chief executive officer, called the cuts painful but said they were "absolutely essential in our current environment." He added: "The long-term answer to Eastern's problems is a revamped labor cost structure."

Eastern, which was acquired last year by Texas Air Corp., has been seeking major wage concessions from its workers and is negotiating with the International Association of Machinists, which represents 13,000 Eastern employes.

The layoffs include both union and nonunion employes but appeared to fall heavily on workers represented by the machinists' union. The company would not provide a breakdown of the cuts, but said that neither pilots nor flight attendants would be laid off. Eastern, which has had troubled labor relations throughout the year, has been losing pilots at a more rapid than usual rate.

Eastern said that an estimated 1,000 workers in southern Florida would lose their jobs in the layoffs. An additional 700 workers in Atlanta are expected to lose their jobs. The rest of the workers to be laid off are spread throughout the airline's system.