FEDERAL agencies used to hire temporary workers in order to get around end-of-year work-force limits. Office of Personnel Management Director Donald Devine correctly criticized the practice as bad management and introduced better controls to remove this artificial incentive for hiring temporary workers. But now that the use of "temporaries" has declined, Mr. Devine is urging agencies to hire more temporary workers. Which policy is better?

The proper balance between career and temporary workers obviously depends on an agency's current assignments. If an agency has a temporary need for an enlarged work force or for employees with special skills, it should either hire temporary workers or employ the needed services by contract. But hiring and training workers costs money, and using temporaries for permanent jobs is generally a bad practice. For most tasks, agencies should, as Congress intended when it created the civil service, employ career workers under the rules established for competitive, nonpartisan hiring.

The new policy removes certain restrictions on hiring temporary workers, allowing them, for example, to stay on the job for as long as four years. Civil service unions fear the policy is meant either to allow the administration to substitute politically sympathetic workers for career civil servants or to lay the ground for further large reductions in civilian workers, or both. OPM says its purpose is only to encourage good management.

In agencies that take their missions seriously and manage their resources thoughtfully, better management might result. But Mr. Devine's primary rationale for urging the hiring of more temporary workers -- that the proportion of temporary workers has declined slightly -- doesn't hold water. After all, the decline he now complains of is the direct, predictable (and not necessarily undesirable) result of two Reagan administration policies: so-called reductions in force, which naturally prompted agencies to lay off temporary rather than permanent workers to the extent they could, and closing the loophole that allowed agencies to avoid counting temporaries against end-of-year personnel controls. Unless an agency has acquired new temporary tasks or is facing more budget cuts soon, there is no apparent reason to step up temporary hiring.

Private companies facing uncertain markets are hiring more temporary workers. But, increasingly, they are the permanent employees of temporary- help agencies that train them and provide full fringe benefits. Temporary workers in government, hired without fringe benefits and other protections and with little chance of permanent employment, are not likely to be committed, protive or adequately trained. OPM's new rules may be harmless or even hpful, but they will bear close watching by Congress.