FROM TIME TO TIME, people ask: "Why does no one these days resign from a government?" The question is asked, of course, of those at the top. It has become extremely rare for a member of the Cabinet or of the highest echelon at the White House to hand in his resignation on a point of principle or even his own misconduct. It is equally true that presidents are now reluctant to fire the top people whom they appoint.

The question is a good one. If one is embarrassing the president whom one serves, or if one is embarrassed by the president whom one serves, one should pick up one's pen and write, "It is with reluctance that I surrender the office to which you appointed me, but . .." There used even to be an art to resigning and to resignation letters.

I think that I am right in saying that political resignations have been rarer in American history than in Britain or any other parliamentary system. The reason is obvious. The members of a government in a parliamentary system are drawn not only from parliament, but from a strong party which is likely to continue to embrace him, while still supporting the prime minister.

The resigning official may leave the government, but he still sits in parliament and has standing in his party. Except in the extremely rare cases when someone is expelled from parliament, or from his party, the judgment is left to the voters in his constituency at the next election. Politicians in a parliamentary system have a political life of their own beyond their appointment to a government by a party leader.

In Britain, a member of a government -- or of the "shadow government" of the opposition party -- sits on the front benches in Parliament. All that happens if he resigns is that he moves to the back benches. One day he is on the front bench. The next day he rises from the back benches, either to explain his conduct which has forced his resignation, or to denounce the prime minister he has just left.

Parliament so sustains the individual political life of one of its members that he may not even have to move to the back benches. If he has a particularly important standing in his party, he may move only to "the front bench below the gangway." The gangway is merely an aisle which divides the benches. It is one of the most honored places for party men who are in opposition to their party.

From the front bench below the gangway, a Churchill might flay his own party and there, indeed, as an old man he sat, sometimes slumped as he quietly dozed, after age had forced him to resign from the office of prime minister. These images -- "the back benches," "the front bench below the gangway" -- are important. They tell of a political life which is independent of a prime minister or a president.

But the member of a government in America -- whether in the Cabinet or in the White House -- is simply the creature of the president. Even if he was drawn from Congress -- as some usually are -- he must give up his seat. If he resigns, therefore, where does he go? To the Ford Foundation? To the World Bank? To Arnold & Porter? (Perhaps even to Harvard, a fate worse than death.) Wherever he wretchedly goes, he must leave the political theater.

This is true even of those who are thrust out of government by the voters. There was something infinitely sad and telling about the three ex-presidents who traveled together on Air Force One to the funeral of Sadat. Stripped of any place of significance in the political life of their country, they preened themselves, among the jelly beans, in their moment of make-believe importance.

A parliamentary system would keep Henry Kissinger in the political theater ever when out of office. But the shuttle diplomat is here reduced to a shuttle celebrity. The waste of political talent and experience in the United States is appalling. No other political system would have allowed Terry Sanford, when he ceased to be a governor, to while away his best years as president of moderately good university.

This waste runs through the whole system. If a senator or congressman is defeated in his home state, he normally cannot, as in a parliamentary system, pick up his bags, travel the length of the country and lay claim to a seat in any other state of the Union. In this vast continent of a nation, he is confined to a single state. It is no wonder in America, given how the system works, that resignations are so rare.

Resigning, as I have said, is an art. (Firing is also an art, of which Truman was a master.) There is the resignation, first, to forward one's own career. A timely resignation on what one at least makes out to be a point of principle can do wonders for one's career. One becomes a hero, the focus of dissent, and one can usually trust to events, not too far in the future, to appear to justify one's action.

But one must, if one is to attempt such a resignation, study one's own hand. One can easily overplay it. In one of the most famous resignations in history, Lord Randolph Churchill resigned, at the height of his youthful career, from the post of chancellor of the exchequer. There was no one, he thought, by whom he could be replaced. He would be asked back, he believed, on his own terms, more powerful than ever.

But the prime minister found a dull but considerable man to take his place -- one J.G. (later Viscount) Goschen -- and the phrase "He forgot Goschen" stands as a warning to all resigning politicians. With filial piety as a young MP, his son Winston took up the cause, the supposed principle on which his father had resigned. "I raise the tattered banner," he said in so many words, "left on the field by another man ..."

But Winston Churchill was then himself very careful about when and how he resigned. (Resigning is a family habit of the Churchills.) When he at last banished himself to the wilderness of opposition -- on two main issues: the granting of a measure of self-government to India and the appeasement of the Nazis -- he did so only on what were to him mighty principles of policy and honor. With an almost unparalleled tenacity of purpose, he embodied not only a cause but a very spirit.

One gazes from such an example -- for Churchill in effect resigned all hope of future office, when he was already a towering figure -- back to the Vietnam war. Where was the resignation on principle which would have electrified the nation? Oh, McGeorge Bundy got out early. Robert McNamara, after giving consistently bad advice, got out late. Even Bill Moyers sneaked out just in time to become a traveling salesman of himself in the media.

But where was the overt resignation on principle? For there is another weakness in the American system. There is no collective responsibility in the Cabinet. A secretary of defense never resigns in protest against the policies of a secretary of the interior. (Or vice versa.) Yet it is just such resignations which compel a public responsibility for the total policy of a government.

Lastly, there is the resignation forced not only by one's own misconduct, but even by the appearance of misconduct, if it too much embarrasses the administration. We demand very high -- sometimes absurdly high -- standards of our politicians. We hold them to account for conduct which is normal in most businesses, even praiseworthy, and is certainly not unknown in the ivied cloisters of our universities.

But if one embarrasses a government by an offense against such standards -- or even by the hint of such an offense -- one should resign at whatever cost to one's own reputation. (And if one so resigns in a parliamentary system, it must be emphasized, it does not necessarily banish one from politics.) But governments engaged in the business of life and death cannot for too long be troubled by a man of repeated poor judgment.

It is a fine line which the president or prime minister has to war politicalk. Bert Lance was a longtime friend of Jimmy Carter. His predicament must have been agonizing, and I personally made allowances for that. When Harold Macmillan at first did not compel the resignation of John Profumo, he said to me later: "I asked him if the reports about him were true, and if a boss cannot take the word of a member of his staff ..."

In short, it should not be left to the boss in such cases to compel the resignation, to fire the man. The man should resign at once and therefore with some honor. A political resignation on grounds of one's own conduct is not an admission of guilt. It is not a moral but only a political act. It says merely that the man considers that, rightly or wrongly, he has become an embarrassment to the government.

The conclusions of all this seem to me obvious. There is no reason why David Stockman should have got out. I happen to detest his policies. But this government would be spineless without him, and all that we now know is that he has been fighting genuine political battles within the administration. It does no harm to have them in the open; it is preferable to a leak. But Richard V. Allen, having once already been forced out of Reagan's campaign staff, ought now to leave. It is simply a matter of pluses and minuses. The end sum, in Allen's case, comes out minus.

As Harold Macmillan once said on another occasion, before firing one of his most loyal colleagues, "Enough is enough"; and with that he sent his foreign secretary to the back benches, where he still pursued his political career.