Mandatory power cutbacks were imposed on about half of Indiana yesterday as Public Service of Indiana, the state's largest power utility, sought to conserve its coal supply. The immediate impact was diminished, however, by the holiday.

Under an emergency order from the state government, the utility directed its 83,000 commercial and industrial customers to cut electricity consumption by 25 percent. Schools and libraries were told to cut consumption by 50 percent.

About half-a-million residential customers in the utility's service area, covering most of central and southern Indiana, were ordered to use 15 percent less electricity than usual. Since Public Service has no way to police residential usage, however, this "order" is essentially a request for voluntary compliance.

Hoosier Electric Co., a small utility serving a few rural counties, imposed similar cutbacks.

In northern Indiana and in other Midwestern states, local governments asked everyone to reduce electricity consumption voluntarily.

Such requests are effective, up to a point. Indiana utilities reported that last week, when Gov. Otis Bowen asked for a voluntary 25 percent cutback, consumption fell by only about 10 percent.

Despite official warnings of serious power shortages if the coal strike continues, the attitude among most people in central Indiana seemed to be "Crisis? What crisis?"

Shoppers thronged brightly lit malls for holiday sales yesterday. At Tippecanoe Mall in Lafayette, the heat was reduced to 62 degrees, but the change was barely noticeable to shoppers coming in from 20-degree temperatures outside.

Factory workers in central Indiana began to feel the coal shortage more directly. Six hundred were laid off at a big Chrysler Corp. transmission plant in Kokomo. Most other firms reported they were cutting overtime, but seeking ways to meet the required cutbacks without layoffs.

An economist at the University of Indiana estimated that 7,000 workers here might be off the job by Friday, and that layoffs could increase sharply next week if coal does not begin moving to generating plants by then.

Nonetheless, union members continue to express support for the coal miners. At the big U.S. Steel works in Gary, the steelworkers scheduled a parade this afternoon to display solidarity with the miners' union.

Since most schools and government offices and many factories were closed for the holiday yesterday, the impact of the power reduction was not sharply felt. Today schools and businesses will have to deal directly with the problem.