Take trash, burn it to generate steam power for a truck assembly plant and air condition the plant all year round; then use a computer to monitor second-by-second operations to cut energy consumption by 7 per cent.

That's what is done at the 1,600-person, four-year-old factory General Motors Corp. opened up today for some three dozen newsmen.

The medium-duty-truck plant boasts what is probably the only successful industrial operation worldwide burning paper, cardboard and wood trash that normally would be used as landfill to cut coal consumption by one-third.

This is how it works: A huge, 125-ton hammermill smashes garbage-free but unsorted waste to potato-chip-size pieces at up to 40 tons per hour. Magnets and forced air separate out metals, and remaining refuse is pneumatically blown to a silo. From there, it is mixed with coal for even thermal output and burned to produce steam.

The steam is the then used for power to air-condition the factory at 80 degrees all year round.

GM estimates the trash burning saves the equivalent of 30,000 tons of coal or 4.7 million gallons of fuel oil per year.

The computer monitoring system scrupulously controls plant operation to eliminate energy waste when starting and shuting down processes such as heating and ventilation systems and paint booths and ovens.

In a short talk following the plant tour, Howard H. Kehr, executive vice president in charge of GM's technical staff, made these points about energy:

Engineers at a GM plant in Athens, Ga., successfully substituted alcohol for natural gas in a heat-treating operation in just three days in a recent experiment. Normally, they would have expected the changeover to take three years, but they moved quickly because of the gas cutback.

The U.S. will run out of oil and gas perhaps by the end of this century. GM is thinking about making "personal transportation" using electricity or electrified coal when that happens.