President Carter apparently has met with room to spare his goal of slimming down the federal work force by 20,000 people by Oct. 1. Carter decided to deflate the bureaucracy last February. He chose a 1-for-2 attrition method as the best way to do it without disrupting vital functions.

Under a freeze order, federal agencies can (with a few exceptions) fill only one of every two vacancies. There was a slight jump in employment after the freeze was announced. That was because many offices -- anticipating the hiring limitation -- promised large numbers of people jobs. But employment has been going downhill since May, according to figures supplied by the Office of Personnel Management.

Because the government is so large, it never knows how many people it has on board at any given moment. However, from June to July the number of full-time permanent employees decreased by 6,182.That means that about double that number of people quit, retired or died, leaving spaces to be filled under the 1-for-2 rule. From February to the end of July, the number of full-time employees on the federal payroll (which was $5,074,799,000 that month) had declined by 14,940.

The actual February-to-October cutback (data won't be available for a couple of months) will be even greater than the 20,000 goal Carter set. Thousands of workers retired set. Thousands of workers retired at the end of August to take advantage of a 7.7 percent cost-of-living raise for retirees.

Carter aides are proud of the orderly job cutback. They contrast it with Republican presidential candidate Ronald Reagan's promise or threat (depends on how you look at it) to slap a total freeze on federal hiring as soon as he is sworn in. Total freezes have a charming political ring, but they rarely work.

Last time there was a total freeze imposed on government (the Senate did it under president Lyndon Johnson), it lasted about 48 hours. Maybe not that long. The Defense Department said if it was deprived of the ability to get top-notch clerk-typists for any length of time, the Russians would soon march down Pennsylvania Avenue. Congress exempted Defense from the freeze. At that time, Defense had on its payroll more than half the federal work force. Next came the old Post Office Department, which said a freeze could delay delivery of Social Security checks, etc.

Exempt POD, the second-largest agency! The Veterans Administration quickly climbed on the exempt bandwagon. It was the third largest federal operation. Then came the Federal Aviation Administration. FAA warned of planeloads of congresspersons coliding in midair if it were barred from replacing retired air traffic controllers. FAA was exempted.

Then the Internal Revenue Service pointed out that if Congress wanted any taxes collected that year, had it given any thought about who would collect them? Congress took the hint; it exempted IRS. Somewhere in all this, the FBI said the nation's crooks would love to see The Bureau frozen. FBI was exempted. And so on down the line.

If the Reagan people plan to freeze the government -- and it sounds like a great idea to many voters -- they had better decide which government services they think will not be missed. When you try to gore the federal establishment, it seems everybody has a piece of the ox.