The U.S. Supreme Court this week upheld an important weapon in the war against drug abuse by validating the use of mandatory tests under certain circumstances.

But there are sharp limits to how far such tests can be pushed without trampling on the rights of ordinary citizens who have nothing to do with illegal drugs.In its first ruling on the constitutionality of drug testing, the high court gave the government broad powers to test federal employees who are entrusted with public safety or sensitive information.

The ruling has no direct impact on the private sector because the constitutional provision at issue before the court - the Fourth Amendment - forbids unreasonable searches and seizures by government officials.

Even so, the Supreme Court action can be expected to set the tone for what is appropriate testing in business and industry as well. Already, on-the-job drug tests are becoming increasingly commonplace, particularly for the biggest corporations.

Certainly it makes sense to allow drug tests for airline pilots, train operators, and bus and truck drivers in view of the great public damage that can be done if their judgment and reflexes are impaired by drugs or alcohol. The same thing goes for drug and alcohol abuse among police officers and firefighters as well as those with access to secrets affecting national security.

But it's hard to see the Supreme Court's action as any justification for routine drug tests of, for example, ordinary clerks in the U.S. Department of Interior, as some officials have been seeking to do.

On the other hand, the American Civil Liberties Union and various other critics are acting as if the Supreme Court had stormed the last citadel of liberty. Some critics go so far as to claim that ordinary Americans might be subject to random drug tests under the new court ruling just because they are injured on the job or happen to drive a car but are never involved in an accident. What nonsense!

Used selectively, tests can act as a deterrent to drug abuse. Used indiscriminately, they can generate a public backlash. The Supreme Court has merely begun drawing the legal guidelines on the use of such tests. Meanwhile, though occasional mistakes will be made, give this country credit for some common sense.