Carter administration reorganizations of the bureaucracy have given thousands of federal workers the option to retire much sooner than they planned, some going out as early as age 43.

More than 40 of the special "early outs" have been approved this year by the Office of Personnel Management. It was also the first agency to use the broad new authority. OPM was created by the Civil Service Reform Act, which split the old Civil Service Commission into several different agencies. Under the act, agencies facing reorganizations may offer limited early outs to employees if approved by the OPM.

Under civil service reform, employees in agencies facing shake-ups can retire - if OPM approves - at any age with 25 years of federal service (either military or civilian combined). They must volunteer for it, and retire within the time period set by their agency and OPM. Workers who take advantage of early outs are usually denied full pensions. They must take a reduction of 2 percent for each year they are under age 55. The early out also applied to employees who are age 50 with at least 20 years of service.

On one hand, the early out can be a blessing to an employee who wants to quit relatively young and begin a new career. On the other, the early out provides agencies with a carrot to ease out people who figure it is easier to take the money (reduced pension though it is) and run, rather than fight or try to hang on under a new political team.

Early retirement was formerly limited to agencies facing major rifs (refuctions-in force and was used sparingly. But it was expanded to include reorganizations as part of President Carter's promise to federal workers that nobody would be penalized or lose a job because of his reorganizations of government. The idea is to make it attractive for senior or long-service workers to quit, thereby cutting the defense outposts on Pacific islands.

Early out retirements were authorized - for limited times this year - for agencies ranging from the Alaska Railroad and the Postal Rate Commission to civilian workers in defense outposts in Pacific islands.

The offer of the early out does not mean that everybody eligible takes advantage of it. For example, during the time it was offered here for employees of the Agriculture Stabilization and Conservation Service, more than 600 workers were eligible. But only 13 actually retired.

Currently, early outs are being offered at the Federal Aviation Administration's associate administration for engineering and development through Sept. 30...National Security Agency for special occupations through Sept. 30...Bureau of Land Management here through Dec. 31 and at the Commerce Department's U.S. Travel Service through Sept. 30. The Naval Weapons Engineering Support Activity is offering ihe early out through Sept. 21. Social Security Administration is offering it to workers at Grade 12 and above through Dec. 31.

Shake-ups are coming in a number of federal agencies and they have requested OPM authority to offer the early outs. Among those requests pending are the Federal Labor Relation Authority, National Park Service and Federal Emergency Management Agency.