Career American diplomats and Central Intelligence Agency aides who can now retire as early as 50 might have to work an extra 10 years to get full pensions under a proposal PresidentReagan will make shortly as part of his new budget package.

Foreign Service staffers at State, USIA and the Agency for International Development as well as many CIA personnel are now covered by early retirement rules. The rules are similar to those for federal firefighters, law enforcement personnel and air traffic controllers -- whose jobs are either dangerous or have a high rate of burnout.

Last week I reported that the administration had decided to exempt employes in those special early retirement programs from any legislative attempt to raise the retirement age for most other civil servants -- from scientists to letter carriers.

But administration officials now say that CIA and Foreign Service personnel will be included, along with rank-and-file federal and postal workers, in proposals to raise the retirement age.

The plan, subject to congressional approval, would reduce pension benefits for most federal workers retiring before age 65, and would require Foreign Service and CIA personnel to work until age 60 to get full benefits.

Most government employes can now retire at age 55 after 30 years' service on pensions equal to 53 percent of their final salaries. Full benefits, calculated on salary and service time, are also available to employes who are 60 with 20 years' service, or 62 with five years' service. The maximum pension -- 80 percent of salary -- goes only to those with more than 41 years' service.

Reagan's plan would require rank-and-file feds to work until age 65 to get full benefits. Those who retired early would take a 2 percent reduction in their annuities for each year they were under 65.

Employes who are 55 or older at time of enactment would continue under the present retirement system. Workers 45 and younger would feel the full impact of the change.

The Reagan plan would not change benefits for most employes under early retirement systems. They can retire at 50 with 20 years service on annuities equal to about 40 percent of salary. That early retirement feature would continue for firefighters, controllers and law enforcement personnel.

But Foreign Service officers, and CIA employes would, if the changes are made, have to work until age 60 to get full benefits. They could still retire earlier than most civil servants, but would have to work 10 years longer than they do under the present system.

The early retirement system was designed by Congress for feds in jobs that are dangerous, sometimes require difficult overseas assignments or produce unusual stress. The early-out system also opens up jobs and promotions for younger workers.

Just why the administration wants to have CIA and foreign staffers work longer is anybody's guess. Foreign Service workers, in particular, are subject to "selection out" -- firing -- if they fail to get regular promotions.

Given the sometimes dangerous nature of Foreign Service work (consider Iran, Lebanon and hot spots in Central America), and the quiet clout of the CIA on Capitol Hill, there is a good chance Congress will reject a higher retirement age for those employes even if it approves it for other workers.