The Army yesterday said it will award Martin Marietta Corp. a potentially key contract to build a nonnuclear air defense system that can be used to shoot down hostile helicopters and aircraft.

The initial $92 million contract will authorize Martin Marietta to produce four test versions of the defense system known as the Air Defense Anti-Tank System. If the system proves successful after a test phase beginning in 1989, the Army will buy 166 of the units at an estimated cost of $1.7 billion.

David Harris, a spokesman for the Army Missile Command in Huntsville, Ala., said the 166 ADATS units would be used to equip Army divisions stationed in Europe. Eventually, he said, the Army has identified a need for 562 units to equip troops in South Korea and elsewhere.

ADATS would replace the Sgt. York air defense gun, canceled by the Pentagon last year because of poor performance. ADATS was developed by Martin Marietta for a Swiss company that was awarded a contract to supply the units to the Canadian military. Some ADATS are being built by Martin Marietta for the Canadians at the company's Electronics and Missile Group facility in Orlando, Fla.

Work for the new contract, which will be formally awarded upon passage of the 1988 budget by Congress, will also be performed at Orlando, a spokesman said.

Martin Marietta also said yesterday it has been awarded a $608 million Air Force contract for continued production of its LANTIRN night navigation and targeting system.

LANTIRN is an electro-optical system that is attached to the fuselage of F15 and F16 aircraft, enabling pilots to fly beneath radar at high speeds.