THE CANADIAN POLICE scandals seem, to an American eye, strikingly similar to the history of abuses that go under the name of Watergate. But the political reaction in Canada is cautious and muted. The present government, under Prime Minister Pierre Trudeau, will certainly survive. The scandals may not even prove to be much of an issue in next year's elections. Yet it is now a matter of record that the Royal Canadian Mounted Police - in effect, Canada's FBI - have been guilty of burglary, stealing political records, illegally opening mail and political harrasment that on one occasion went as far as arson. The Trudeau government knew all about it from the beginning.

The difference in political consequences, down here and up there, has everything to do with recent history. In late 1970, you may remember, terrorists in Quebec seized two hostages - the province's minister of labor and a British diplomat - and murdered one of them. In the midst of that crisis, the Canadian government discovered that it knew nothing about the kidnapers or their organizations or their political milieu. The government told the Mounties thatit could not afford to continue in that ignorance.

Everything that has happened since then reflects the torment of a government trying or cope with the threat of terrorism. The transgressions of the Nixon White House were aimed either at the Democratic presidential campaign or at subversion that existed nowhere but in the imagination of Mr. Nixon himself. In Canada the terrorist episode was brief, but it was real. For Ottawa the recollection of the dead minister, Pierre LaPorte, is still vivid.

Since then, of course, a wholly legal and democratic separatist movement has won control of the Quebec provincial government. This challenge has now become the overriding preoccupation of Canadian politics, and the people who support national unity are not much inclined to pursue Mr. Trudeau on issues that might weaken him in dealing with Quebec. The Mounties' misdeeds have evoked little open outrage, except among the French nationalists of Quebec at whom most of this harassment was directed.

Canada and the United States offer the endlessly illuminating contrast of two very similar societies with different political histories. Canadians did not experience first-hand the war in Vietnam, with its erosion of citizens' trust in their government and its heightening of sensitivities to official intrusions. It's a healthy thing, in our view, for citizens to be wary of their government - although Vietnam was a bitter price to pay for an education. Canadian attitudes toward the Mounties are very similar to American attitudes two decades ago toward the FBI and the CIA. Whatever the Mounties' offenses, there's one thing that you have to say for them: They did it all terribly ineptly. The revelations so far indicate that the illegal operations were uniformly ineffectual. Even more important, they were unable to avoid public exposure. Those are very good signs. The time to start worrying is when the political infiltration succeeds, the harassment works, dissidents lose the elections - and never a word is heard about the methods of the police.