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.