Resignation over matters of principle remains so rare an event for high American officials that you can count the major occurrences in this century on one hand.

Each time the resignation immediately became a great problem for the president in office. Each time the resignation came over specific incidents. Now Alexander M. Haig Jr. has entered that select company, with certainly equally serious consequences for the president he has repudiated.

He also has broken the historic pattern.

In 1915, William Jennings Bryan resigned as Woodrow Wilson's secretary of state in protest over Wilson's reaction to the German sinking of the British liner Lusitania off the coast of Ireland. In 1973, Elliot L. Richardson resigned as attorney general, as did his deputy William D. Ruckelshaus, after refusing to carry out Richard M. Nixon's orders to fire Archibald Cox, the Watergate special prosecutor, during the so-called "Saturday Night Massacre." In 1980, Cyrus R. Vance resigned as Jimmy Carter's secretary of state in protest over the president's approval of the disastrous military expedition to free American hostages in Iran.

Haig's resignation Friday as Ronald Reagan's secretary of state was different from these. He resigned, as his carefully constructed statement makes starkly clear, in protest over the entire direction of the president's foreign policy.

His use of the past tense to describe his philosophical and professional break with Reagan was most telling, and deadly. "I believe that we shared a view of America's role in the world," he said, and that "we agreed that consistency, clarity and steadiness of purpose were essential to success." But, and again note the past tense, it was clear to him that the foreign policy "was shifting from that careful course."

Seldom, if ever, in American history has a top official dissented so completely and openly with a president's overall approach to foreign affairs. These are reasons enough to give the Haig affair a special place among the cases of U.S. resignations in protest carried out in full public view.

There are others, perhaps more significant.

From the day he was elected president, Reagan has carried an even greater burden than normal for a chief executive.

He took office after a period of unparalleled turmoil affecting all of American public life, and most directly the presidency. Five straight presidents before him, men unalike in character, temperament and viewpoint, had been unable to remain in office through two full terms. National leaders representing all shades of opinion, ideology and background, whether left or right, liberal or conservative, Republican or Democrat, black or white, northern or southern, had been destroyed, disgraced or in one way removed as factors in public debate. The Vietnam war and the Watergate scandal added to the collective sense of national unease.

Out of these elements grew an underlying public desire for national stability and continuity that contributed strongly to Reagan's election, and intensified public hopes for him. His burden has been to repair that cumulative national damage and restore that sense of national stability and well-being.

The Haig resignation tears at those hopes and efforts for special reasons.

Haig is no ordinary Cabinet officer. He is at once the best known and most experienced of the president's top circle of advisers and policymakers. Before joining the Reagan administration, he already had become more than a footnote in recent presidential history; he was part of the main text.

On these grounds alone his resignation becomes significant. But the timing and circumstances of his departure are even more troubling. He breaks with the president over foreign policy substance at a moment when world events are especially perilous. Worse, they appear in danger of growing out of control. The departure of America's secretary of state at such a fragile moment internationally is only certain to heighten the feelings of instability.

Unfortunately, the president's handling of this incident did not help matters. Rather than explain calmly and fully the reasons for Haig's departure, the president offered no explanations at all. He himself appeared shaken. His manner was halting. He seemed befuddled. The sight of him shrugging off reporters' questions, as if perplexed, as he boarded his helicopter to go to Camp David shortly afterward reinforced a feeling of disquiet.

Thus, the greatest impact of Haig's resignation could well be on the public perception of this president's ability to demonstrate he has conditions fully in control and still the doubters who wonder whether he is up to the job. The danger for Reagan is that the public might come to agree with Haig that his presidency is "shifting from that careful course" he had promised to chart.

That doesn't mean Haig has dealt Reagan a blow from which he will be unable to recover. But it certainly means this:

At a time when people hunger for steadiness and stability, they are getting instead another signal that things are falling apart.

Americana, Hard Times, Paradoxes Department:

A faculty administrator of the University of Chicago's Graduate School of Business tells me the following:

This spring's crop of master of business administration graduates was able to choose among three or four good job offers each. The average starting salary for the new business school products was $32,000. The top starting salary offered a member of the class was $55,000.

"It was all handed to them on a silver platter," says the faculty administrator, wondering aloud whether these new young business employes could have any conception of what the rest of the economy is like or appreciate the hardships being endured by so many others across the country today.