SPIRO AGNEW, a lesser crook in the Nixon den of thieves, ended his farewell address to the nation on a note of reassurance. Quoting from a remark made by James A. Garfield upon the assassination of President Lincoln, Agnew said. "Fellow citizens, God reigns and the government in Washington still lives."

The federal government has survived the death of Lincoln by 108 years. Whether constitutional democracy will be able to survive the administration of Richard Nixon is entirely another question.

Chaos is not too strong a word to describe the present condition of American government. For the past five months it has been able to function only marginally; for the past week it has functioned not at all. During his press conference last Friday night Nixon pointed to his decisive action in the Middle East as evidence of the continuing vitality of the government, but the skepticism aroused by his declaration of a military alert points only in the opposite direction.

When an American president puts the armed forces on a full alert and half the population believes that he acted only to shore up his crumbling domestic political position, a claim that the government in Washington still lives is negligent optimism at best.

The number and seriousness of the rumors flying around Washington this week are further indication of the crisis of confidence. Congressmen are saying that Nixon is about to declare martial law; aides are passing the word that Nixon is starkraving mad and undergoing shock treatment; underlings in the executive are saying that Nixon is Mafia-connected and that's why he paroled Jimmy Hoffa and Gyp DiCarlo. The rumors are terrifying not only for what they say but because we have no means of judging how far-fetched they may be.

The confidence of the American people in the ability of the government to govern has eroded at a progressively increasing rate. The failure of nearly one-half of America's qualified voters to turn up at the polls last November is indicative of a lack of faith in anyone's ability to govern properly.

But it is not only the governed who lack confidence; the governors and the prospective governors are beginning to believe that the thing just doesn't work.

John Herfort graduated from Harvard in 1968 and from the Law School three years later. He worked as a clerk in the First Circuit Court for a year, and when that job ended he went to work in the Department of Justice under Elliot Richardson.

Herfort resigned from the Justice Department when Archibald Cox was fired and when Richardson resigned. He talks about the standstill that the department finds itself in now; he talks about things like the need for dynamic leadership and the reform of an ossifying bureaucracy. He resents the fact that his successors at Harvard might look down upon him for working in the Nixon administration. "Government," he says, "has to go on."

But Herfort is getting out. He's thinking about coming back to Boston and working for a newspaper. Government must go on, but now it will go on without John Herfort and many more like him.

Garfield was right when he said the government in Washington still lived. It survived because people believed in its ability to survive. It survived because people believed it should survive.

But now there is the unmistakeable impression in the capital that if one could get by the policemen and the fences surrounding the White House, one would only have to blow on the building and sit back to watch the whole thing crumble to the ground.

BEING a practical-minded nation, Americans and particularly American politicians have forgotten the theory behind republican institutions. They have forgotten that republican government is supposed to rest upon the consent of the governed, and, now that the people have been effectively cut off from the government and its doings, the government rests on grounds so shaky that the slightest shock could send the whole thing into the sea.

And the shock has come. But what is to come next?

If the problem were only Richard Nixon, the answer would be simple. Once we get rid of Nixon and get a half-way decent man into the presidency, the problem would be repaired and government could again begin to function. Unfortunately, nothing is that simple nowadays.

There is no question that Richard Nixon is a problem. He is a liar who has caused the slaughter of millions of Asians. He has tried to deceive the American people, he has tried to ignore their laws, he has tried to subvert their rights and he has attempted to gather the power of their government into his office.

Richard Nixon is definitely a problem, but he is not the problem.

THE attempt to centralize power in the executive and the use of illegal and quasi-legal means to achieve that centralization is not unprecedented. The process has been an on-going one since the 1930s. Nixon is quite right to point out the extensive use of wiretaps in the Kennedy administration; by the same token he could defend his phoney military alert by saying that Kennedy pulled a similar trick during the Cuban missile crisis to make his failure at the Bay of Pigs look excusable.

As power increasingly becomes the property of the executive, Americans become increasingly alienated and isolated from their government. They feel that government is out of their hands, and quite rightly they conclude that it doesn't matter a damn what they think or do about the course of American politics.

Now at least they can write to their congressmen and say that Nixon should be thrown out of office. Chances are that Nixon won't be thrown out, but even if he is they will feel no closer to the political structure. For the millions of Americans who voted for Nixon a year ago, his impeachment and conviction will only mean the replacement of one bad man by another who may or may not be less bad.

The government in Washington can not survive under these circumstances, and under these circumstances, and under these circumstances the government should not survive. Still there is the question of what will go in its place.

AMERICA'S low tolerance for turmoil and its self-generated alienation from politics may well cause the trend towards one-man rule to accelerate so that executive rule becomes accepted in name as well as deed. One cannot afford to overlook the possibility that the illusion of republicanism will be dispensed with and that the United States will set out on the road of dictatorship and autocracy. It is not an enviable possibility, but a real possibility nevertheless.

Frighteningly enough, the other possibilities are harder to imagine. Can we manage another constitutional convention? Can we manage to reformulate our government so that it respects our civil rights and responds to our wishes?

The notion of a new constitutional convention is an intriguing one. After 200 years, why not redraft the charter? These who wrote the first document were not gods, but men. They could not forsee the course that the country would take and they did not expect the republic to produce men like Nixon. From our new perspective, we might write a constitution more conducive to republicanism in the last half of the twentieth century.

But constitution-writing is a reflective affair, and we may not have the stuff to do it well. But unless we do something quick, we won't be able to do anything at all.

The way things stand in Washington, the government of republican illusions is about to fall. America will be governed in any case, but the question is by whom. If not by the people, then by a strong executive. These are revolutionary times, and we must decide now whom we want to win the revolution.