THAT THE RUSSIANS have been spying again is not exactly man-bites-dog news, but that Canada has just caught and ordered expelled no fewer than 13 Russians, including a full third of the embassy staff, is unquestionably eye-opening stuff. This cell was accused of trying to penetrate the Canadian secret service and perhaps other reaches of the government.Canada is one of those Western nations that, in a spirit of East-West amiability, has allowed the Kremlin to increase the numbers of its embassy and trade personnel, never mind that known KGB operatives have often filled the new slots, and to play down instances in which Soviet officials have been caught, if you will, red-handed. There is a whole school of thought holding that such permissiveness encourages espionage and diminishes what incentive the Russians may have to tread the straight and narrow. In any event, in Canada the Russians went too far.

One aspect of Canada's handling of the incident deserves special note. Expelling the spies, the Canadians announced that since none of their people in Moscow have been spying, they would react to the Kremlin's retaliatory expulsion of any Canadian by replying tit-for-tat. There are 28 Russians on the diplomatic list in Ottawa, and about 12 Canadians on the list in Moscow. Our own guess is that the Russians will not go far beyond huffing and puffing. They would not wish the Canadians to enforce diplomatic parity. They have abiding reasons of state to ensure continued access to the Canadian wheat market. The more that Western nations reduce their own direct spying in communist-bloc states, for whatever reason, the better position the Westerners are in to be tough about communist espionage on their own soil.

For the government of Prime Minister Pierre Trudeau, this instance of Soviet "respect" for his detente policy can hardly be welcome. To diversify Canada's trade and, especially, to take up a foreign-policy stance distancing Canada somewhat from the United States have been his goals. Yet a display of vigilance in defense of Canadian security cannot be altogether irrelevant, politically speaking, to a leader facing not only possible elections this year but also a deepening crisis over the country's federal integrity. This is not to say there is a phony note detectable in the government's retaliation to the Soviet espionage provocation. Leaving domestic politics aside, the heavy-handedness of this Russian espionage operation would have been grounds enough for Canada's stern response.