Today's auto special: compact cars at $3.01 a pound

Compact automobiles are the ''best buy per pound,'' according to the latest ownership and operating-expense study by the Hertz Corporation. At $3.01 a pound, the compact car replaces the traditional standard-size car that had held the ''best value'' honor for at least a decade.

''Big cars, now in second place at $3.06 a pound, still lead both the subcompact units, now $3.14, and intermediates, now $3.26,'' the Hertz study reports.

Ten years ago Detroit's big cars set buyers back only 99 cents a pound, intermediates $1.03, compacts $1.12, and subcompacts $1.33, the report notes.

In its yearly expense study, Hertz now puts the total ownership and operating cost of compacts driven 10,000 miles a year and kept five years at 43.28 cents a mile, down 1.4 cents from 1982. This is the first drop since the price-control era of 1971, when expenses edged down three-tenths of a cent per mile - to 18.7 cents.

The study credits reduced loan rates and lower fuel prices for the decline.