If the people of Montgomery County really want safe busing for school children, they should look to performance tests rather than alcohol and drug tests {"Montgomery's Schools to Test Drivers for Drugs," Metro, Jan. 9}.

Alcohol and drug tests administered without cause are an invasion of privacy and are too often inaccurate. Also they do not accomplish their purported function of ensuring that school-bus drivers are fit and ready to perform well on the job.

Once-a-year and pre-employment testing tells us only what a person has taken in the preceding day or two (or month, perhaps, in the case of marijuana). It cannot distinguish between substances taken on the job or on one's free time. It tells us nothing about the driver's ability to perform safely the next day at 7:30 a.m. or 3 p.m.

Alternatively, performance testing each time the driver climbs into the bus will ensure that he is fit for work. This could take the form of ignition interlock devices installed in each school bus or one of the other performance tests under development for airline pilots and nuclear workers.

The greatest advantage of performance testing is that it weeds out not only those too drunk or drugged to pass the test, but also those who are too tired, emotionally upset, hypoglycemic or impaired by antihistamines and other legal drugs to drive our kids safely to and from school.

I am more fearful of a bus driver who is not fully attentive to his duties because of a sleepless night, an emotional argument with a spouse before leaving for work, a skipped breakfast or a cold remedy taken in the morning, than of one who is alert and fit now but smoked a joint last Saturday night.

What is the real aim here? Do we want to improve safe driving of county school buses, or do we want to control the private, off-the-job lives of county employees? BETTY KING Alexandria