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Itsy-bitsy cars for little errands. . . . A three-year experiment in West Lafayette, Ind., could change urban America's driving habits. Some 15 to 20 families in a Purdue University project will do errands and commute to nearby jobs in imported Japanese micro-mini cars equipped with two- to three-cylinder engines.

Computers will keep tabs on engine stress and fuel use, as researchers seek ways to improve the efficiency of the small cars. Drivers will not take trips of more than 30 miles or drive at speeds greater than 40 miles an hour. A fleet of regular-size cars will be available for longer travel.

The cars cost about $3,000 each and are about half as expensive to operate as most subcompacts. General Motors plans to market similar cars within the next few years.

Purdue researchers predict many city drivers will like the arrangement. The cost of maintaining a shared car for out-of-town trips could be less than owning a second, larger car.m