BRIAN MULRONEY and his Conservative Party have won a tremendous victory, one that, for the first time in many Canadian elections, runs the full width of the country. It's a sweep on a scale that submerges the established regional patterns. Most French-speaking voters went the same way as most English-speaking voters. The industrial cities went with the western prairies and oil fields. As John Turner, the defeated prime minister and Liberal Party leader, put it, the returns were "absolutely convincing."

Those returns confirm a Canadian consensus that the great figure of the country's recent politics, Pierre Elliott Trudeau, had stayed too long -- and that Mr. Turner, who succeeded him two months ago, showed too little capacity to change. When Mr. Trudeau first became prime minister in 1968, his country was moving rapidly toward a crisis that, under less able leadership, might have torn it apart. A powerful separatist movement had formed in the French-speaking majority of Quebec, and there was a real possibility that Canada would dissolve into two -- or perhaps three or four -- independent countries.

Over the 1970s Mr. Trudeau successfully restored a durable national unity. But the Trudeau method required a lot of bargains and concessions back and forth across the English-French line. When the crisis was finally over, he left a great many Canadians convinced that they had been used not quite fairly. All of those irritations have been aggravated over the past four years by the further strain of poor economic performance. The 1982 recession was far more severe in Canada than here.

That suggests the job ahead for Mr. Mulroney. He has to find ways to reconcile the people -- especially in the West -- who consider themselves to have been injured by the vigorous application of Mr. Trudeau's nationalism. He has to find ways to get the economy growing faster, with higher investment to generate more employment for a young and growing population.

He isn't likely to copy much from the Reagan variety of conservatism. Canada has a long tradition of low defense spending and generous social benefits. Nothing in his campaign suggests that he intends to change either of them much. With budget deficits already larger in proportion to the economy than in this country, Mr. Mulroney does not have a lot of room for maneuver on taxes.

But Canada's similarities to the United States make it an instructive example of political alternatives. In the Trudeau years, Canada was preoccupied with its own ethnic divisions. Now its political energy will go chiefly into the struggle to find an acceptable balance between economic growth for society as a whole and economic security for its people as individuals. Since all the other industrial democracies are now engaged in the same search, Mr. Mulroney's kind of conservatism will have more than local interest.