Looking for the perfect gift for the federal executive who has everything? Consider a Ronald Reagan 120-day appointment calendar. Not as silly as it sounds. Read on:

When President-elect Reagan is sworn in on January 20 the countdown will start for 6,800 of the government's top-paid career executives. Those chiefs, once well insulated from political climate changes by civil service security blankets, are no longer quite so fire proof. At least they won't be after May 19.

Career federal executives, who have traditionally been off-limits and technically untouchable by politicians, will become much more touchable next year under new rules set up, ironically, by the outgoing Carter administration.

The $500,000-a-year career people are now nearly all members of the Senior Executive Service. As such they will have sanctuary for only 120 days after Reagan takes over or their new boss comes on board. After that . . . nobody knows exactly what to expect.

The elite SES corps did not exist four years ago, so it has never had to undergo a change in administrations. The Civil Service Reform Act proposed by President Carter was designed to make the career bureaucracy "more responsive" to the party in control of the White House. Supergraders who volunteered for it -- membership is mandatory for new enlistees -- traded in much of their tenure and security for the chance to get ahead, to get 20 percent bonuses and for more rewarding, challenging assignments in a corps that stresses rank-in-person, rather than grades.

SES members who get bad marks from performance review boards [which include some political appointees as well as fellow career executives] must be transferred to a new function or job, lose their chance at pay raises for that year and can be bounced out of the SES. In most cases they land at the same pay level in the career service at Grade 15. But a demotion from the SES is certain to be an ego-bruising thing, and all but ends that person's hopes of ever climbing back up the civil service totem pole. Most SES members are right in the middle of performance reviews now. So far as is known, none has been rated so badly as to lose his or her job or merit transfer. But that could happen after the next review.

The next time for review will be 120 days from Jan. 20, or about May 19. (If you like trivia, be advised that May 19 is the first anniversary of another big explosion in Washington, the 10-megaton volcanic blast at Mount St. Helens in Washington State. Some might find that significant).

To ensure that new political bosses don't start chopping executive heads too soon, the Civil Service Reform Act prevents them from involuntarily transferring career SES members for 120 days from the date they, the political chiefs, take office. The act also bars any new performance appraisal of SES members -- a good one that could mean a bonus, or a bad one that could mean bye-bye -- for 120 days following the inauguration of the president. So you have, in effect, two separate 120-day periods. One, which governs the issuance of new performance appraisals, begins Jan. 20. The second 120-period starts when the career executive gets his or her direct political boss.

Whatever happens, the 1981 year means the beginning of a whole new ball game for U.S. executives. Fortunately for them, the Reagan talent scouts will be kept busy for a while. As reported here yesterday the new administration will have about 6,000 top-level jobs to fill almost immediately. a