Fairchild Industries Inc. beat out giants Rockwell International and Cessna to win a potential $1.6 billion contract to design, develop and manufacture the Next Generation Trainer aircraft for the U.S. Air Force.

Including options, the contract, announced by the Air Force and Fairchild yesterday, calls for production of 650 of the craft between now and 1992. The jets will be built at Fairchild's Hagerstown, Md., and Farmingdale, N.Y., plants.

Fairchild, which for months had been considered the leading contender for the contract, was the only bidder to build a full-scale mock-up and to flight-test a 62-percent-scale model, company officials said.

Chairman Edward G. Uhl said yesterday that the company's Fairchild Republic Division, producer of the NGT plane, probably will not hire additional workers, but the contract will help to keep the current work force employed. Anticipated cutbacks in the production of the A10 "close-air support" jet for the Air Force has caused some layoffs at the Hagerstown and Farmingdale plants.

Fairchild is a large aerospace, telecommunications and manufacturing company with revenues of more than $1.2 billion annually. Among its products are the A10, parts for Boeing's 747 and 757 passenger aircraft, components of the Space Shuttle, and assorted nuts, bolts, fasteners and molds.

James R. Wilson, senior vice president and chief financial officer, said yesterday that returns from the NGT program, while not enormous compared to the A10 contract, would be a significant source of earnings for Fairchild during the 10-year contract period. Uhl indicated that Fairchild could profit from other, non-Air Force sales of the aircraft, such as to foreign buyers.

The Air Force had challenged bidders to come up with a trainer with, among other specifications, greater fuel efficiency than the Cessna-built T37, which has been used for training since 1958, when fuel was relatively cheaper.

The initial contract to Fairchild is for $104 million to be used for design, development, fabrication, testing and delivery of two test aircraft. Options for 54 planes come after that, then further options would call for building 650 planes.

Joining Fairchild in its bid was Garrett Corp. of Phoenix, which won Air Force approval to produce engines for the trainer.

The New Generation Trainer is a twin, turbo-fan, jet-powered craft with side-by-side ejection seats. It will cruise at 35,000 feet and 300 knots, according to Fairchild.