President Carter has approved a plan that would prohibit federal government agencies from firing any employees as a result of efforts to reorganize the bureaucracy. The plan would also restore grade and pay levels to thousands of employees who already have been demoted this year in various routine shifts.

Most of these demotions have occurred as a result of shakeups that seem to accompany all new administrations and as a result of routine "desk audits" - evaluations that determine whether a federal employee is being overpaid for the work he is doing.

The new job protection plan, conceived by the Office of Management and Budget and the U.S. Civil Service Commission, will be officially circulated throughout the federal government today.

The fear of demotion or layoff has panicked many people here, where 347,000 people work for the federal government. Although there have been minireorganizations by some Cabinet officers, rumors of the big Carter reorganization yet to come have caused severe morale problems in many agencies.

The recent suicide of a Commerce Department worker at his office was, some friends and colleagues believe, triggered by depression resulting from his demotion.

Federal officials believe the new guidelines may block layoffs being planned by the Agency for International Development here, and for Housing and Urban Development workers in the field.

But the same officals said they doubt the President's guidelines will help any of the 800 CIA employees whose jobs are being abolished because of "major mission changes" and internal realignments.

The new job protection guidelines are part of a broad package designed to soothe bureaucratic resistance to reorganization already under way and planned. The guidelines also follow the President's promise to the 2.6 million civil servants that none of them would be hurt by his shakeups and streamlining plans.

Since that February promise, many workers have been downgraded or told they will be. The demotions result from agency shakeups or audits showing that jobs are overgraded through no fault of the worker. The promise of grade restoration contained in the new guidelines covers both kind of "no fault" downgradings.

The vehicle for protecting employees from downgradings is a bill already before Congress. It was originally designed by the White House to cover only employees involved in reorganizations. Now, the President says he will ask that it include all "no fault" demotions, and that its protection be made retroactive to january 1 of this year.

Under the complicated plan, employees scheduled for demotion would retain their pay and grade for two years. Their job would be earmarked for demotion by a process called "red circling." During that period the employee could try to find another job at his current grade, or the agency might restructure the job. If not, the position and the employee would be downgraded.

Then the employee would get 50 per cent of whatever the annual October pay raise was for other civil servants until his salary equaled his new, lower, grade level.

Workers whose jobs are either abolished or changed because of reorganization would be reassigned to other work, the guidelines say, with "reasonable amounts of training at government expense . . ."

The job protections, to be enforced by OMB (which controls dollars) and the Civil Service Commission (which oversees personnel practices) also say that agencies can't fire a worker just because of reorganization. The agencies first must make a bona fide job offer, "preferably at the same grade" and that the offer must be refused before the worker can be dismissed.

Federal employees transferred to other cities would have all "necessary travel costs paid by the government. And those transfers must be timed," the memo says, "to provide reasonable periods for employees to make personal arrangements."

While the job protection plan covers workers demoted in 1977, it does not provide for rehiring of employees fired earlier because of agency reorganizations or cutbacks. It does, however, urge agencies to give priority consideration to workers hit by previous reorganization layoffs, and authorizes special actions that may be taken regionally or by occupation, to provide special placement service for individuals.

An official said yesterday the new guidelines might cause some "very temporary" doubling up of personnel in some agencies where reorganization plans had called for big job cuts. "The alternative," he said, "was to kick people out, or downgrade them, and we knew we couldn't do that because the President promised it wouldn't happen."

The new job protections will force some agencies that had planned lay-offs to rely almost exclusively on attrition to cut employment. It is likely that many federal departments will freeze hiring, and promotions, until they determine the impact of the job guarantees on their reorganization plans.

The guidelines are careful not to give job guarantees to employees who work at agencies where layoffs may be dictated by budget cuts, by military base closures or by major mission changes. The Carter administration is planning a major round of military base closures next year.

Officials said they felt it would have been "unrealistic" to shut down an Army base, or a Navy installation, if the workers had to be kept on.

These employees will, however, get priority job placement and the protections against demotions will apply to them as long as they have their jobs, officials said.