Eaton Corp. is opposed, violently opposed, to an expected federal government decision this week ordering installation of the air bag in all new automobiles.

Secretary of Transportation Brock Adams has promised to announce his air bag decision on Thursday, at a luncheon of the Washington Press Club. In comments over recent months, he has indicated that he favors mandatory use of the saftey devices.

Eaton is the primary enterprise behind development of the controversial device and has spent more thn a decade of design, engineering, development and test work on the product.

Years back, Eaton was showing film clips about the air bag at national automotive engineering meetings, before auto companies took it seriously and before the name of Ralph nader became a household word in the Motor City and elsewhere.

Further, Eaton stands to become a major supplier of key parts of the pilow-like safety device which fits into a car's dash or steering wheel and explodes in th ewink of a eye to cushion occupants during a crash.

If the airbag were to become a widely used item on cars, Eaton would almost assuredly begin making a profit in selling those parts to the automakers, and thus recoup its $20 million-plus work on the idea.

Why then the opposition? Simply because the top management at eaton, a multinational corporation with $1.8 billion sales in 1976 and some 50,000 employees, has come to believe that a premature, forced introduction of the air bag will make it fail.

According to marshall Wright, vice president for public affairs, the only experience with air bags so far has been with what are essentially "almost handbuilt prototypes."

"If you try to go from zero to ten million, the result of that kind of effort are predictable," he said. It is "utter folly" to try that kind of a "galvanic leap," he added.

It is widely believed in automotive circles that Adams will abort contracts signed by former Secretary of Transportation William R. Coleman Jr., requiring a large-scagle test of the devices. The presumption here is that the dievice will be ordered into production in some fashion.

The contracts signed by Coleman would require General Motors, Ford, and Mercedes-Benz to manufacture, promote and sell 200,000 pllus 1980 and 1981 model cars equipped with air bags.