IT IS REALLY like one of those mad adventure stories in which the central characters, after experiencing the most improbable and hair-raising series of mishaps, turn up on schedule wherever they were expected after all - without a word about what went on. So here we are . . . right on schedule: At the noon hour of the 20th day of the first month of the fourth year, like clockwork, this nation swears in a newly elected President and Vice President. And give or take a few silk hats and cutaways, it will be the traditional, ritual affair this year. You would hardly guess that anything peculiar or disruptive had occurred in the interval - that, for example, the Constitution had proved sturdy enough to help boot out of office the last president to stand on those steps and swear to preserve and defend it, or that on this day we will be swearing in our - yes - fourth Vice President in four years.

Political time plays tricks on the mind. When events are compressed it expands, or seems to anyway. How many John Mitchells ago was Richard Nixon sworn in for a second term? Was it two Sam Ervins before or three McGoverns after the Saturday Night Massacre? Our point is merely that the last election and inaugural seem eons back in time.It is as if the nation had covered a hundred years in four. We have, as we all like to say, put that behind us - the constitutional crisis, the gathering consensus that a sitting President had to be removed from office, the event itself and its aftermath. And this is Jimmy Carter's day, not John Sirica's or Leon Jaworski's. But the inauguration that takes place today - whatever its traditional forms and business-as-usual aspects - is different from those that went before, and it is different precisely because of the terrific upheaval that occurred in midterm.

Jimmy Carter swears today to "preserve, protect and defend the Constitution of the United States." During the past four years, the people whom he will serve have learned a lot more than they ever knew before about both the vitality and the vulnerability of that charter. They have had a close call. They have seen their system of government shaken and imperilled - and also, ultimately, vindicated. They have had occassion to observe as well that no charter or document is proof against subtle subversion.And they have surely gained a new appreciation of the importance of simple human decency in the conduct of public business, whether it was demonstrated by the courageous people who rose above political interest to follow conscience in the Watergate affair or by the man who inherited the wreckage and helped put things together.

We do not mean to lecture Jimmy Carter on all this. No one needs to. He rose to the presidency precisely on an understanding of how these events and perceptions had affected the people whose votes he was asking. We bring it up because we think that some reflection on where this nation has been in the past four years is essential to understanding the meaning of the ceremony that is taking place today. Inaugurations are rituals. They tend to look alike. This one is different. And it is different because of the turmoil and reaffirmation of constitutional values that preceded it. The oath has been given a new force. It is more than just words. People and Presidents now know something about our constitution and its demands that they may not have thought about before. So Jimmy Carter will get up there right on schedule and raise his right hand and say the familiar words . . . just as if nothing had happened. Four years - 1973 to 1977: As we said, it has been some adventure.