President Carter still has the impression that he is in charge of the federal government. His voice is soft but his manner is firm. He has sounded a gentle warning to the vast federal bureaucracy that he expects renewed vigor, that they must cut out their extravagances, that changes are coming. As evidence he means business, he fired Maj. Gen. John K. Singlaub for criticizing his decision to withdraw troops from Korea.

The President has the power, indeed, to fire generals, to formulate policies and to direct the nation's affairs. But one day he may wake up to the fact that those faceless bureaucrats are really running the country.

Their ultimate strength is the finesse, the unobtrusiveness, by which they rule. So gently, gradually and invisibly do they tighten the bonds that the President may never fully appreciate the extent to which he is in their grip. They will be ingratiating; they will always say, "Yes, Mr. President." But all the while, they will manipulate the policymaking machinery.

Though we revile bureaucracy for its bumbling and futility, in fact our Presidents have been no match for it, and so it rentlessly encroaches upon them. Part of the reason for this historic impotence is that much of the time Presidents don't know precisely what they're talking about, while the bureaucracy does. They have to rely on the bureaucracy for information, for expertise in drafting their measures; and the civil servants can usually show them 10 practical reasons why their ideas won't work.

Presidents are also outgunned by the troops they inherit. Jimmy Carter invaded Washington, for example, with a fragmentary force of no more than 1,200 men and women. Yet they were thrust into command of a world-wide civilian force of $2,832,000 bureaucrats and a military force of 2,100,000 volunteers.

The bureaucracy also has a million telephones connected to hundreds of pressure groups, with which to stir up opposition against any directive the bureaucrats cannot stomach. They have also perfected the technique of solemnly pondering directives from on high, forever reviewing and revising the fine print, on the assumption that an unwanted directive will go away if they study it long enough.

In the end, Presidents depart, whil the bureaucrats abide. Any points the bureaucrats lose in the early rounds, they get back later, when the administration of the law or the order is entirely in their hands. A few deft changes of emphasis and al is as before.

The recall of Singlaub from South Korea has been compared to the firing of Gen. Douglas MacArthur two decades earlier. Editorials have hailed President Carter's success in disciplining Singlaub in contrast with President Truman's failure to restrain MacArthur. The end result, however, has been the other way around.

MacArthur's public statements were crafted to skirt overt insubordination yet permit insurrectionary inferences to be snapped up by a great following. He has seen by millions of fundamentalists as a mountain peak silhouetted against the lighting, the last bearer of the true flame.

But ultimately, MacArthur went too far in his statements; on April 11, 1951, President Truman boiled over and fired him, setting off a daily heightening typhoon of national emotion. Yet MacArthur, to his undoubted dismay, faded away almost as quietly as his oratory had prophesied.

Singlaub's firing was less spectacular but more typical. The military bureaucracy paid lip service to the President but united behind the general. He appeared to Capitol Hill like MacArthur to repeat his criticism of the President's policy. But unlike MacArthur, Singlaub did not fade away. He would up instead with a coveted new assignment as chief of staff of the Arm's largest command.

It remains to be seen whether the military bureaucracy will get its way in Korea, as it did in Vietnam. The late President John F. Kennedy was opposed to pouring troops into Vietnam. He wanted to form a crack counterinsurgency force, which could train the South Vietnamese in jungle fighting.

Overriding the opposition of the Pentagon bureaucracy, he established the Green Berets. But the unit became a military orphan, shunned by the big brass. The word quietly spread the service with the Green Berets was the wrong way to advance a military career.

In the end, the bureaucratic brass dumped manpower and firepower into Vietnam as they had wished. They also fought the conventional war they had favored - against, unfortunately, an unconventional enemy. The Vietcong's crude style of warfare, not unlike that used by our own forefathers to wrest independence from the British, confounded those who fought by the book. Thus, many Americans died in South Vietnam on the altar of the military bureaucracy.

In 10th century Egypt, a slave caste called the Mamelukes was entrusted by the sultans with the public administration; the Mamelukes soon became the new line of sultans. The Czars, if they could reduce a whole population to serfdom, were not able to subjugate their bureaucracy once it got established. Even Mao Tse-tung could not prevail over the bureaucracy he established.

The betting is that Jimmy Carter, too, will wind up more the tool than the tamer of the bureaucracy.