A federal study of electric utility billing practices, initiated after complaints of excessive charges during the 1977-78 coal strike, calls for an overhaul of wholesale rate schedules.

The study by the staff of the Federal Energy Regulatory Commission said that using existing rates in emergency situations such as the coal strike "may produce charges unsupported by costs."

The FERC has jurisdiction over wholesale transactions -- those between producers and distributors of electricity. The study covers such transactions.

Rates charged retail customers are set by individual state regulatory commissions. Presumably reductions in wholesale prices can lead to retail price cuts.

The FERC staff study, released yesterday, said "there may have been some improprieties in the billing of power and passthrou4gh of costs in fuel adjustment clauses" during the strike.

"These, however, did not add significantly to the cost of electricity to consumers," the study added.

Most billings followed existing rate schedules and so were as proper as the schedules, according to the study.

The report focuses on the so-called "adders," percentage factors added to fuel costs in preparing bills for energy supplied by one utility to another.

These originally were designed to recover relatively fixed costs, according to the report.