The 12-foot-high letters atop the Mead Corp.'s 28-story downtown tower that spell out the company's name are no longer illuminated after dark.

Four of the then elevators in the $1.8 billion industrial firm's headquarters are shut down, and employes are being asked to walk between floors rather than use the elevators still working.

These moves by Mead, a diversified manufacturere, are mirrored by numerous firms in this industrial center as the growing gravity of the continuing coal strike threatens to shutter much of the area's economic life.

Similarity, electric conservation effects are visible around the state. In many areas, they are more drastic than here, where Dayton Power & Light Co. had as of yesterday a relatively plentiful coal supply of 59 days.

About 25 miles away in Middletown, which is served by the hard-oressed Cincinnati Gas & Electric Co., the giant Armco steel plant has shutt off three pollution control devices as an electrically-saving device to help meet the utility's call for a voluntary 25 percent cutback.

Armco, one of the nation's largest steel producers has adopted some potentially costly measures to save energy. These measures involve turning off standby motors, which normally are left idling to ensure continued production should the main units fail.

Standby units are employed, for example, in the slab mill where hot steel ingots of up to 40 tons are converted into flate slabs. With the standby motors off, it would take longer to activate them, thus running the risk of extending production losses in the event of a breakdown.

These measures are saving energy, stretching dwindling coal supplies and delaying the need for large-scale, mandatory cutbacks that could cripple the production of some of the nation's largest industries.

Such cutbacks would be instituted well before stockpiles run out. Dayton Power & Light, for example, has planned rotating blackouts for all areas, and electrical reductions of 50 percent or more for large users when the coal supply hits 25 days. In other parts of Ohio, some utilities were reported near the 30-day supply mark at the end of last week.

General Motors, for example, is faced with cutbacks at five key Ohio plats that make parts needed to sustain production elsewhere. Should these plants, served by coal-short Ohio Edison, close, than 300,000 General Motors employees would be laid off.

A GM shutdown would be especially felt in Dayton, where the nation's largest auto maker is the city's largest employer, with more than 30,000 workers.

The auto maker, thought, has been implementing energy conservation measures since the oil embargo, and is hard pressed to cut further. "There aren't any major actions you can take to get substantial reductions overnight because we've been finding them all along," GM spokesman Jerome Bishop said.

Among the measures adopted in Southern Ohio GM plants are reducing the speed of ventilation motors serving offices.

GM has, however, cut overtime at its Norwood assembly plant in suburban Cincinnati, where the fast-selling Chevrolet Camaro and Pontiac Firebird are produced. All told, 26 hours of overtime production a week have been slashed. Bishop said that it is hoped the production can be made up later.

Other manufacturers are trying to avoid production cutbacks by substituting machinery that does not use electrically for these that do. That desire has produced a surge in sales and rentals of diesel-powered portable generators and air compressors. Air compressors run a high percentage of plant machinery.

The result has been a shortage. "If I had them, I could make a million dollars this month," remarked Raymond T. Zent, parts manager for a Dayton firm that sells stationary air compressors that run only on electricity. Zent cited a hight number of calls, many of them the Cincinnati area, for diesel or gasoline-driven units which his firm doesn't have.

If mandatory cutbacks of substantial size ar imposed - 50 percent or more are an imminent possibility - production loss and large-scale layoffs are inevitable. Indeed, compaines will be pulling out most if not all the stops to save energy.

Mead, for example, plans to close down two more elevators, cutbacks come, vending machines and lights in offices with windows to the outside if 50 percent reductions are imposed.