IF YOU HAD to perform a task 1.2 million times a year, isn't it reasonable to assume that every once in a while you'd do a less than perfect job? Surely this is true even of the most diligent, highly trained and well-motivated workers. Isn't it logical, then, to assume that the Army, which gives 1.2 million drug tests to officers and enlisted men every year, is capable of fouling up -- say, once in every quarter of a million?

That's the point two young lieutenants are trying to make in an effort to save their careers. Steve Becker and Jay Drummond were tested last April at Fort Belvoir, and the Army says the tests showed high levels of cocaine in their systems. Both had fine records in the service, had passed drug tests before and were on notice that they would be tested during their three-month tour at Fort Belvoir. But as far as the Army is concerned, the test is conclusive, and now neither man has any future in the service.

For all we know, the findings may be accurate, but the procedure is flawed. The consequences of a positive test are so great that there should be a backup mechanism, a way of double-checking that will protect the individual when mistakes are made either in the chain of custody or in the lab. Dr. William Manders, a retired Air Force officer who was involved in developing the first testing programs, has suggested a change of procedure that would resolve this problem with little trouble or additional cost simply by taking two samples for testing, the second for use in confirming evidence of drugs found in the first.

In the criminal justice system there are numerous safeguards to protect the rights of the accused and an understanding that occasionally a guilty man will go free under rules designed to ensure that an innocent man is not convicted. In drug testing, the presumption is that the test is right, and the accused has the burden of proving his innocence. A positive finding, however, is so difficult to contest that innocent people occasionally are made to suffer. There is little chance that the armed services will abandon mandatory drug testing, but there is every reason to make the procedures fairer and more foolproof.