The corporate armies that build tomorrow's weapons are riding high

Ford Aerospace calls it the Sergeant York Gun System. But the hero of the Argonne Forest, who with just a handful of men crushed a German machine-gun battalion during World War I, would be hard pressed to find a resemblance between warfare as he knew it and warfare as it is being engineered in the defense plants of Orange County.

The Sergeant York, known acronymically as DIVAD, for ''division air defense, '' is a radar-directed automatic gun system to defend forward maneuver battalions, the M-1 tank, and infantry fighting vehicles against attack aircraft. The system is mounted on a modified M-48A5 tank chassis.

A demonstration film shows a York-equipped tank in simulated action, rolling inexorably across a field, its distinctive antenna, spinning around, reaching out for signals.

War, like almost every other human endeavor, is a high-tech endeavor, and should Armageddon ever come, weapons and equipment made in Orange County will be on the front lines.m

You wouldn't exactly call Orange County's defense-related aerospace contractors recession-proof if you had seen them reeling as the Vietnam war was winding down.

They expanded rapidly during the early 1960s, peaking in 1967, and later virtually collapsed before making a sturdy recovery.

But the defense producers march to a different budgetary drummer. They seem not to be subject to quite the same business cycle as Orange County's other high-tech enterprises - for good or bad. If the Reagan administration is putting more stress on defense than its predecessor, it doesn't make that much difference in the near term.

What the defense companies make is years in the planning. Rockwell International, for example, expects it to take five years for full-scale engineering development of the guidance and control system of the new Missile X (MX), now in its fourth year.

A Bank of America forecast, predicting that Orange County will get $13 billion in government defense contracts in 1983, suggests it's not clear what effects these contracts will have on aerospace employment. As of 1980 aerospace accounted for 35 percent of the county's manufacturing jobs.

The major companies - Rockwell, Hughes Aircraft, Ford Aerospace, Northrop, and McDonnell Douglas - are represented by branch installations here with headquarters elsewhere, generally in Los Angeles County. They have virtual armies of employees: 12,500 at Hughes and 10,000 at Rockwell, the largest two private employers in the county. (Rockwell's legions include other, nondefense electronics people, though.) Generally dating back to the 1950s and clustered in Fullerton, Anaheim, and Huntington Beach, they made up the first wave of major industrialization here.

What these mighty armies do, basically, is build the electronic controls for weapons systems, and also defense-related communications systems.

Hughes, whose Fullerton-based Ground Systems Group is the biggest group in the company, is noted as the ''Cadillac'' of defense contractors. Its products are more expensive but worth it.

Hughes enjoys a good balance among the different branches of the service, and between domestic and foreign business. The result is a pretty steady business, even by the standards of recent years.

The Ground Systems Group's products include what are called ''command and control systems.'' You've seen the sci-fi movies where the Leaders of the Free World watch Soviet missiles zooming toward them on a computer display map of the whole world? Well, if those scenes ever get played out in real life, it's likely to be on Hughes-made equipment.

At Hughes, they also make super-heavy-duty military computers that have to be built to sustain all the shocks of battle, under conditions where the user can't just pick up the phone and call a service technician if the system goes down. Secure radio communications, including field radios enabling a soldier to let base know his position with the flip of a switch, are also part of the program.

Besides DIVAD, in production in Newport Beach and Irvine, Ford Aerospace's Orange County operations include production of guidance systems for the Sidewinder family of missiles - named for a snake that tracks victims, like its namesake weapon, by sensing their heat.

Rockwell International, whose Orange County base is in Anaheim, is providing the inertial navigation systems for the Navy's submarine fleet, including the new Trident, as well as the above-mentioned MX guidance systems. Spokesman Tony Longo says the company projects 20 percent growth over the next five years. Rockwell also has a microelectronics research and development center in Anaheim.

Northrop Corporation has some 1,500 people in Orange County, mostly involved with electro-optical sensors, and with checkout equipment for the Polaris, Poseidon, and Trident missile systems. Northrop is also involved in making launchers, loaders, and fins for the improved Hawk missile system.

The McDonnell Douglas Astronautics Division, in Huntington Beach, 6,000 -strong, is a mixed bag of defense and civilian operations: solar energy research and work on the manned space program. It also builds the Delta rocket, used to launch communications satellites, and is working on a classified project for the Army, the Sentry missile program.