Nearly 70 percent of the civilian jobs in the Defense Department are now protected from contracting out because of an "off-limits" sign that Congress tacked onto the military budget before it recessed.

The action will slow contracting out--the replacement of civilian federal workers with private-sector workers -- because nearly half the federal civilian work force is employed by the Army, Navy or Air Force. The three largest employers in the Washington area are Navy, Congress and the Department of Health and Human Services.

Congress took the action at the request of career and political executives at the Pentagon. They were concerned that replacing civil servants with contract employes could rob the military of in-house capability during national emergencies and decrease the control of civilian and military managers over key support functions.

Contracting out has stepped up since the Reagan administration took office. Although some civil servants landed jobs with contractors -- often at higher salaries -- the action also resulted in layoffs for many others.

All agencies have made studies of their so-called commercial-type activities (those are jobs that are in "competition" with the private sector) to see if they can be farmed out. Targeted jobs range from clerical and blue-collar fields to printing and building security jobs.

The new Defense Authorization Act says, "It is essential for national defense that Defense activities maintain a logistics capability (including personnel, equipment and facilities) to insure a ready and controlled source of technical competence and resources necessary to insure effective and timely response to a mobilization, national defense contingency situations and other emergency requirements . . . . "

Congress has ordered the Army, Navy and Air Force to identify all "core functions" (those directly related to national defense support), to report them to the House and Senate Armed Services Committee by April 1, and to exempt them in most cases from contracting out plans. Congressional sources say that could cover as many as seven of every 10 jobs.

Other federal agencies have not yet been exempted from contracting out, and many functions of nondefense units either have been or will be selected for contracting out later in this fiscal year.