HOW OFTEN do you pick up the paper, read a story about a foreign country, and say to yourself, "Now there is an ally"? Not very often -- but yesterday was an exception. The story was amazing. Canadian Embassy officials in Tehran had conspired to give refuge to six American diplomats who had eluded capture at the American Embassy on Nov. 4, hidden them safely for some 12 weeks in the hostile city, and finally spirited them out of the country with Canadian passports under the cover of shutting the whole Canadian mission down.It was not simply that it was an exceedinly slick and well-executed operation, one worth its own thriller. It was that a friendly nation, at no small risk to its own interests as conventionally conceived, went way out on a limb for an ally and did something truly selfless and honorable.

That's not all. The operation was hardly an aberrant act for Canada. Since the beginning of the double crisis of Iran and Afghanistan, the Canadians have been acting in a way the United States could wish all its fiends would take as a model. For Canada, wheat exports have even more economic and political importance then they have for the United States, but Canada quickly joined the grain embargo against the Soviet Union. The Canadians were among the first to support the idea of a boycott of the Moscow Olympics. These steps were taken, moreover, at what is unquestionably a most difficult time for the government of Prime Minister Joe Clark. He faces elections in just a few weeks, and the easy political thing -- as a fallen leader we remember might have put it -- would have been to avoid any move exposing him to the nationalistic allegation that he was dancing to an American tune.

Canada is a self-respecting nation with serious differences with the United States. In fact, the chief daily foreign business of any government in Ottawa is to pursue those differences, and the current set will not be washed away by good feeling alone. Yet there are not so many times when countries (including this one) put principle first and perform in a manner deeply helpful to a neighbor or friend. It is an important event, and Americans will surely be grateful and remember. Canada has acted the waywe would like this country to act, were the circumstances reversed.