Fairchild Industries Inc. last week said it was separating the operations of its Maryland composites-and-bonding plant from the those of Fairchild Republic, its Long Island, N.Y., division that makes the T46A jet trainer and subassemblies for other aircraft.

The company took the action, effective Jan. 1, to stress that the Hagerstown, Md., plant will continue to operate on its own merits, regardless of whether the T46A program is canceled by the Air Force and Fairchild Republic is closed. The Air Force had proposed dropping the aircraft from its 1987 fiscal year budget, but the jet still could be reinstated by Congress.

"We believe the bonding center has the capability of competing for new business on its own in its special field of metal-to-metal and composites bonding," said John W. Townsend, a senior vice president of Fairchild Industries and head of its aerospace group. "Its management should have the freedom to pursue these opportunities and be responsible for the results of its own initiative."

The Hagerstown plant does metal-to-metal and composites bonding on components that are then made into wing or door subassemblies, principally for the C5B Air Force transport, Boeing 747 airliner and the Saab SF-340. All of these contracts are due to expire in 1987, unless there are additional orders. The plant already is pursuing subassembly work on the planned Air Force C17 transport.

Fairchild Industries and officials of the United Auto Workers Amalgamated Local Union 842 also came to agreement on a new three-year contract effective Jan. 1. About 515 out of 650 employes are union members, but the contract called for all employes to make equal concessions, a company spokesman said.

"We know from recent experience that we have not won certain contracts because we weren't competitive," said Townsend. Neither the company nor union officials would give details of the new contract. But the Hagerstown Morning Herald reported recently that the its terms include an 8.5 percent across-the-board wage cut for all bargaining employes, an immediate freeze on raises tied to an increase in the cost of living, and the elimination of five of 14 paid holidays.