Fairchild Industries Inc., based in Chantilly, Va., and most commonly known as an aerospace company, yesterday announced that its two largest aircraft businesses were up for sale as part of a major restructuring of the company.

The announcement comes on the heels of losses of $82.3 million on sales of $196.8 million in the second quarter of 1985 ended June 30 and after selling two of its most profitable communications subsidiaries.

The two aircraft subsidiaries for sale are Fairchild Republic Co., based in Long Island, which manufactures the T46A jet trainer and other aircraft, and Fairchild Aircraft Corp., of San Antonio, which makes commuter planes.

Those aerospace operations include about $400 million out of about $900 million in the company's sales in 1984.

Fairchild President Emmanual Fthenakis said at a New York meeting with financial analysts that the company cannot successfully pursue all of its diverse operations, which include communications and electronics.

"We will not do justice to all of these opportunities by continuing to pursue all of them, so we will have to make some choices," Fthenakis said. Among them are the outright sale of the companies or finding "a partner willing to invest" in either of the operations, he said.

A complete divestiture of some operations is more likely than a partnership agreement since the "key thrust" of the company's new direction is to concentrate on expanding the company's communications, electronics and space businesses, according to Fthenakis.

"The areas of growth are not aviation," he said.

The company intends to quickly reduce its short-term debt of $115 million and is open to outside sources for financing of expansion, he said.

Analysts said Fthenakis' new Fairchild organization may bear little resemblance to the company of only a year ago.

Joe Campbell, an analyst with Paine Webber Mitchell Hutchins, said, "He's got a billion dollar company, and it's going to be a $600 million company. It's going to be a different company.

"It's not an aerospace company, and it's not a communications company," said Campbell, especially after the divestiture of the company's 50 percent stake in two profitable communications subsidiaries, American Satellite Co. of Rockville and Space Communications of Gaithersburg. The company sold its stake in the companies last August for $105 million to partner Continental Telecom Inc.

Despite the sales of those two companies, communications "over time will be the dominant part of the company," said Campbell, with Fairchild using "stable" revenue from its commercial and industrial businesses such as tooling for plastics and industrial fasteners to fund its expansion.

"Initially, you will have a very small diversified company, and it is not going to look all that shiny," said one analyst.

"The long-term strategy is clearly to become a fast-growth communications and electronics company, but it's going to take a lot more than lip service to get there, it's going to take time."

The company's communications, electronics and space businesses, which include avionics equipment and spacecraft subsystems, have been growing at a rate of about 25 percent to 30 percent a year, and last year contributed about $103 million to overall sales.

Fthenakis said Fairchild would "exploit" opportunities in telecommunications and build on its newly formed partnership with $3 billion French conglomerate Alcatel-Thomson by offering "end-to-end telecommunications services . . . and private networks" for business customers.

The company's financial trouble has been a result of unforeseen problems in its aircraft businesses, say analysts. The company has reserved $135 million to cover losses from its Saab Fairchild-340 turboprop airline project because of higher costs, slow sales and efficiency improvements. The company is also writing off another $21 million in losses -- on top of the $28 million it recently reported -- on the T46A program because of high costs and unexpected engineering developments.

The Defense Department recently proposed cancellation of the multimillion-dollar program, which was counted on to be a main cash generator for Fairchild. The Air Force last month announced it was halving its $8 million a month payments to Fairchild Republic for production of the jet and spare parts because of "numerous management and production deficiencies."

Fthenakis said the company was committed to meeting its obligations and had already done a lot to turn those operations around.

Fairchild is negotiating with Saab Scania AB to "lessen" its participation in the commuter plane venture. Fthenakis said Fairchild Aircraft Corp. is now profitable after three years of losses.

Fairchild stock closed at 9 7/8, up 1/2, yesterday. The stock closed at 16 3/4 Dec. 31, 1984.