The Federal Railroad Administration took the only sensible course Thursday when it called for mandatory drug testing of all railroad workers.

Though the plan does not require congressional approval, it won't take effect until after it has been discussed in public hearings around the country.While some rail workers object to the mandatory tests, the plan is in their best interest. After all, drug abuse by train crews can cause train wrecks - and passengers aren't the only ones to die in the wrecks.

The need for the mandatory tests of all railroad workers is clear. Railroad workers are now tested on the basis of "reasonable cause" - meaning only after an accident or when supervisors suspect that a worker is abusing drugs.

What's wrong with the present system? Simply that it puts the responsibility for spotting problems exclusively on supervisors, who can't be expected to be experts about drugs. Indeed, the symptoms of drug abuse can more easily be masked than those of drinking.

After recent accidents, testimony indicated that some rail employees arrived at work "clean" so they wouldn't be tested, then took drugs into the locomotive and used them there.

Before 1985, 16 percent of autopsies on railroad employees killed in train accidents showed traces of drugs or alcohol. Since testing on the basis of reasonable cause began in 1986, the positive test results have been 5.1 percent for drugs and 0.75 percent for alcohol.

Those figures mean that drugs are being used by one person in 20 working on railroads.

Despite the generally impressive safety record of railroads, the risks are still higher than necessary. If mandatory tests are what it takes to make the rails even safer by curbing drug abuse, so be it.