Fairchild Industries yesterday reported the largest loss in the aerospace company's history.

The Chantilly, Va., company had net losses of $167 million ($13.17 a share) on revenue of $856 million for the year, compared with earnings of $1.3 million (loss of 82 cents) on revenue of $819 million in 1984.

The company reported net earnings of $3.8 million (6 cents) on revenue of $246.8 million in the fourth quarter of 1985, compared with a loss of $22 million ($1.86) on revenue of $243.8 million for the same period a year ago. A change in estimated tax benefits related to losses in all of 1985 was credited for the quarter's earnings.

For all of 1985, the company reported a loss from continuing operations of $194.4 million.

In the last year, the company has encountered turbulence in its aircraft businesses because of higher costs and slow sales. In a major restructuring last October, Fairchild put its two aircraft subsidiaries, Fairchild Republic Co. -- maker of the T46A jet trainer -- and Fairchild Aircraft Corp. of San Antonio, up for sale.

The company also sold its 50 percent share in two profitable communications subsidiaries, American Satellite Co. of Rockville and Space Communications Co., to Continental Telecom Inc. of Atlanta, its communications partner in the ventures.

Fairchild also cut losses in 1985 by becoming a subcontractor instead of a partner to Saab Scania AB of Sweden on a project to manufacture commuter airplanes. Write-offs and reserves established on two troubled aircraft programs, the T46A trainer for the U.S. Air Force and the SF340 Saab-Fairchild joint venture, were largely responsible for the year's losses.

Fairchild Republic Co., the Long Island division that makes the jet trainer, had substantially lower sales in the quarter as its A10 spares business declined, and there were no offsetting deliveries and sales for the T46A jet trainer.

Though Fairchild is producing the first 10 jet trainers under contract to the Air Force, the Reagan administration has asked Congress to eliminate virtually all funds for the T46A aircraft as part of the president's 1987 budget. The budget includes no additional purchases of the aircraft and only $10.8 million for research and development. It is uncertain whether Congress may again set aside funding for the trainer returned in the budget.

Wall Street analysts said yesterday more write-offs may be in the offing for the $900 million company if Congress decides to drop the trainer.

"Nothing can be discussed about earnings until we talk about the restructuring of the T46," said Joe Campbell, an analyst with Paine Webber Mitchell Hutchins. "They have their work cut out for them in getting it back in the budget -- if they don't get it back in, they can't operate it as a viable business because the overhead at Republic is too big."

That would mean closing the plant and more write-offs, he said. There are currently no interested buyers for the plant. Fairchild has made a commitment to keep the division operating.

First Boston analyst Wolfgang Demisch said earnings were "a satisfactory result on balance, but we'll take it as it comes." Demisch attributed the increase in overall revenue to the company's other businesses, such as aerospace fasteners.

Fairchild stock closed yesterday at 9 1/8, up 1 1/8 with 134,700 shares outstanding.