Washington ? The hair, saliva and sweat of federal workers could be tested for drug use under a new government policy proposed Tuesday that eventually would set a standard for private companies.

The planned changes, long sought by the testing industry, reflect government efforts to be more precise in its drug screening and to bypass attempts to cheat on urine-based tests. The testing of hair, saliva and sweat will not be required, but would be available as an option to government agencies that screen workers and job applicants.

The agency is soliciting public comment on the plan for the next 90 days. A final rule would be issued afterward.

About 400,000 federal workers, such as those who have security clearances, carry firearms, are involved in national security or who are presidential appointees, must undergo testing. Others are tested only if they show signs of drug use or are involved in a work-related accident.

But because standards are followed by regulatory agencies who conduct testing in industries they oversee, the action affects about 6.5 million of the 40 million workplace drug tests done each year by U.S. employers.

Saliva testing, done using a swab that looks much like a toothbrush but with a pad instead of bristles, is best at detecting drug use within the past one or two days.

Hair testing, in which a sample about the thickness of a shoelace is clipped at the root from the back of the head, allows detection of many drugs used as far back as 3 months.

Sweat testing, in which workers are fitted with a patch that is worn for two weeks, is used to screen people who have returned to work after drug treatment.