Fairchild Industries Inc. yesterday said it will sell its 50 percent share in two satellite communications subsidiaries that had been considered the company's leading growth opportunities.

Continental Telecom Inc., an Atlanta communications company that owned the other half of the two joint ventures, will pay Fairchild $105 million in cash for full ownership of American Satellite Co. and Space Communications Co.

American Satellite of Rockville provides private and general satellite communications services; Space Communications of Gaithersburg provides satellite communications to the Air Force, the National Aeronautics and Space Administration and other government agencies.

Fairchild, which has its headquarters at Dulles Airport and major facilities at Germantown, Md., decided to sell its interests in the companies to consolidate its other businesses, said Emanuel Fthenakis, president. "We are addressing the same market with more than one company," he said. "The main reason is to consolidate our activities and address these markets with our wholly owned subsidiaries."

Analysts said yesterday the move showed Fairchild was unwilling or unable to invest the large amounts of capital required to continue to expand Amsat and Spacecom because of troubles in its other operations.

"The company's financial condition is rather leveraged; this is a way of bringing down debt and there was already a buyer for those businesses," said one analyst who asked not to be identified. The company has sold off other operations in recent months, the analyst said, including its industrial fastener business and a commercial aircraft-seating maker.

Analysts said more divestitures could be in the offing. "Their record indicates maybe there are more divestitures to go," said one analyst. "Though, with this move they have gone a long way towards turning around the balance sheet, and there is certainly no rush to sell anything else at this point."

"My own personal opinion is that they didn't want to step up to the table with a $150 million investment for a new satellite system Amsat would have needed over the next three years," said Robert E. LaBlanc, a telecommunications analyst and former Continential executive. Fairchild has faced stiff competition in its aircraft business, said LaBlanc, and needed to conserve its capital for that end of the business.

"With the recent reversals Fairchild has had in the aircraft businesses they run, they were reluctant to put up the capital," he said. One-third of the profits the space communications companies generated were pumped back into paying off debt, and the remaining two-thirds were split among Continental and Fairchild, he said.

Amsat has long been the major competitor of Satellite Business Systems, a business communications service that recently was sold to MCI Communications Corp. by International Business Machines Corp. Amsat has been profitable for three years, unlike Satellite Business Systems, which has been operating at a loss for some time.

Amsat transmits regional editions of The Wall Street Journal, The New York Times and other newspapers and has won a large number of government contracts.

Spacecom owns and operates the tracking and data relay satellite system for NASA, provides communications to the Space Shuttle and is building a $122.8 million communications network for the Air Force.

Fairchild Industries, the eighth-largest public company in the Washington area, manufactures commuter aircraft, makes aircraft components and tooling for plastics and has telecommunications and satellite interests. Last year, it earned a net profit of $1.3 million on revenue of $898 million.

Amsat generated $72 million in total revenue and earned Fairchild $2.1 million in profits in 1984, according to the company's annual report, and Spacecom earned the company $5.5 million on revenue of $1.2 billion.

Fairchild also has launched two joint-venture telecommunications companies with Alcatel Thomson, a French telecommunications conglomerate with annual revenue of $3 billion.

Fthenakis said Spacecom's NASA project already was completed and that Fairchild would remain a team member on the Air Force communications system project. Fthenakis said Fairchild would continue to develop network services such as Amsat's, but said spinning off Amsat relieved the company of having subsidiaries compete with each other. The Alcatel Thomson joint ventures, which will specialize in shared tenant telecommunications systems, had planned to start providing the same networking services that Amsat specializes in.

"Amsat also does a lot of general services and we are not very much interested in that; it is very close to what MCI does in private-line services," Fthenakis said.

The spin-off is a perfect fit for Continental, LaBlanc said. "Fairchild is an airplane and electronics manufacturer. Continental is a communications operating company and these are communications businesses -- it fits in exactly," he said.

Fairchild closed at 14 3/8 on the New York Stock Exchange yesterday, down 1/8. The sale announcement came after the close of trading