Key federal officials -- especially political appointees -- spent a lot of time last week writing "commitment letters."

This is not part of some romantic revival by the Carter administration. Rather, it is a pragmatic attempt to get in under the wire, to be "home free," in case the president slaps a freeze on government hirings or promotions.

The bureaucracy's rumor mill is working overtime with the news that Carter will impose a freeze. Maybe as early as Monday or Tuesday. When and if it comes, it will be part of a broad federal belt-tightening operation that is partly economic, partly show-biz politics. Whatever the reason, the idea of a freeze has government officials sweating.

If Carter presses the freeze button, he will do it quickly to show labor and management (and the voters) that he is serious about slowing inflation. If he freezes federal hiring, something he can do on his own, it will slow or stop the federal hiring machine, which takes more than 250,000 people on board every year.

If there is a freeze, and it follows past chills, it would allow agencies to promote or hire only those people who received "commitments" prior to the actual date the order is issued. Hence, the heavy typing loads and heavy mail sacks leaving government offices last week.

Hiring freezes are not popular with career federal managers. They point out that the freezes aimed at cutting government via attrition rarely work the way they are supposed to work. Most strip agencies of clerical and secretarial workers, the lowest paid, who have the highest turnover. Also, during previous federal freeze periods, the attrition rate drops as people hold onto jobs rather than retire or move elsewhere.

Savvy bureaucrats realize that the White House does not like to advertise a freeze in advance, whether it involves federal hiring, wages, prices or whatever. That is because people anticipating a freeze take action before it comes. In the case of the government it means a rash of commitment letters before the hiring gangplank is pulled up.

Even when the secret is kept, however, key employes and officials still learn about it. Some are tipped off because they have a need to know. Some get word through friendly senators and representatives. Others are warned of a coming freeze so they can bring more of the faithful into the federal fold before the cutoff comes.

A quick freeze next week could have some dramatic short-term results and savings -- more than in previous years when presidents Johnson, Nixon and Ford tried them.

The savings from a freeze at this time would result from an abnormally large number of retirements that took place in February. Normally between 8,000 and 12,000 people retire from Uncle Sam each month. But February's totals will be higher -- much higher. That's because a 6 percent cost-of-living raise (for retirees) went into effect yesterday. To be eligible for it, people had to be retired by Feb. 29.

Nobody in government knows how many people retired last month. But a similar cost-of-living situation a few years back produced a bumper crop of 50,000 retirees in a single month.

The freeze hasn't happened, yet. It will not be certain unless and until Carter announces it. But this is a town that lives off of, and reacts to, rumors.

If the high-level rumor mill -- which triggered the rash of "commitment letters" last week is accurate -- we should know it soon. Like tomorrow or Tuesday.

Meantime, if you are expecting a federal job, watch your mailbox carefully, over the next few days. And if you were one of the 20,000 people expecting a promotion anytime soon, make a wish -- retroactive to last Friday -- that somebody put it in writing.