Cambridge, England — It isn't illegal to leave Britain without seeing Cambridge. But it ought to be. That's the kind of wild exaggeration you get when writers talk about places truly important to them. There are those of course who look coldly at the outside of King's Chapel and compare it to a sow lying on its back, dismiss the gray misty loveliness of centuries-old buildings seen in the early morning, and hurry off to Oxford. But for me Cambridge has become one of those memories to take out and look at from time to time: a mixture of youth, history, and incredible beauty.
Probably the best way to see the university is to get hold of a good guidebook (''Cambridge,'' with text of Michael Hall and photographs by Ernest Frankl, the Pevensey Press, for instance) and then take your own slow time wandering through the quadrangles, absorbing the atmosphere. But don't, whatever happens, miss King's Chapel or fail to walk along the backs, where the college grounds reach the river.
If it is term time, look at the college notice boards for times of plays and concerts and meetings and for entertainment (the board at St. John's had a sign recently: ''Pay just one pound for an acquaintance to be handcuffed to the Senate House railing whether they like it or not.'') Try to find time for the college choirs. (You will be welcome, for instance, at Evensong.)
Because the buildings only tell half the story, I asked John Rutter, director of music at Clare College, to explain what goes on behind the scenes.
First of all, he said, travelers who appreciate the difference between the university and the colleges get the most out of their visit. People, he said, are apt to stand among the colleges and ask to be directed to the university. ''You have to tell them - it's all around you.'' In fact the university is rather like the United States. The colleges, each one jealously independent in some ways (choosing for instance, their own students and staff), form the federation that makes up the university.
When the colleges were founded back in the Middle Ages, religion and learning went hand in hand.
''You can see that legacy to this day in the architectural layout of the colleges - literally a cloistered layout,'' Dr. Rutter said. ''Some would say that the life lived in them was monasterial until quite late on.''
Most Cambridge colleges admitted only men (though many of them were founded by women), but in the early 1970s a few adventurous colleges opened their doors to women. It proved not to be such a dangerous practice after all (no pregnancies, no lowering of the standard, no neglect of studies), and now nearly all colleges have a mixed student population except for one or two, like Magdalen, which, Dr. Rutter points out, thinks of itself as a gentleman's club, like those in London.
A great improvement as far as he is concerned is that now he has a mixed choir to conduct at Clare and the ''deep throat, growling sound of an all-male choir'' has gone forever.
Dr. Rutter had one very important warning. ''Please don't be misled by all those old buildings. Because Cambridge is old it doesn't mean it doesn't work. Don't mistake occasional (traditional) shows for the fabric of everyday life. In a changed world some sense of established things is important. Students in the serious business of studying can devote 14 hours a day in peace and quiet with all their daily needs taken care of. There is no need to change - they got it right the first time. After all, the important thing about Cambridge is that it works.''