Periodic auto inspections to spot potentially dangerous mechanical defects do not cut accident rates or the number of injuries, according to a study published by the American Enterprise Institute.

The study, by W. Mark Crain, professor of economics at Virginia Tech, found that "there are no detectable (nonrandom) differences . . . between those states with periodic inspection programs and those without." Moreover, it made no difference whether inspections were once or twice a year, nor whether the inspection stations were government-run or private.

Currently, 27 states and the District of Columbia require some form of inspection annually, checking over 76 million vehicles each year. Seven states require twice-a-year inspections, and 10 rely on spot checking. Excluding the cost of repairing vehicles that flunk, inspections cost owners $200 million a year, Crain says.

But only one accident in 20 is caused by mechanical failure, he notes. Eighty percent are caused by human error, with environmental conditions, such as rain or snow, the second most common cause.

Congress in 1966 authorized the National Highway Traffic Safety Administration to require states to adopt an inspection program for all registered vehicles. But, Crain concludes, "These findings . . . warn costly nationwide program without good information on its likely effects."