CANADA'S SUPREME Court has now moved the country a little closer to a resolution--for better or worse--of a profound and unsettling constitutional quarrel. The question is whether the country is to evolve toward a national state with a strong federal government in Ottawa, or toward a loose confederation of regions and local interests. Prime Minister Pierre Trudeau has devoted his long career to the principle of federal primacy, but things do not appear to be moving in his direction.

There's a connection between these strains and the suddenly strained tone of the conversation between Canada and the United States. The Canadian government is trying to reduce the degree of American ownership of Canadian industry, particularly in the oil and gas fields, and American businesses are vigorously protesting. The Canadian ambassador speaks of a "creeping confrontation." The U.S. State Department accuses Canada of unjust discrimination against Americans, and hints at "countermeasures."

It's fair to say that the Canadians have pursued their new industrial policy in a style that sometimes seems deliberately abrasive--awakening suspicions in this country that Mr. Trudeau is trying to strengthen the Canadian national impulse at Americans' expense. But if you say that, you also have to add that Canada continues to run a very open economy with far greater foreign ownership than most other countries would tolerate, including most of the United States's closest allies. Americans own some 70 percent of Canadian oil production. What do you suppose the atmosphere in this country would be if foreign ownership of American oil were one-fourth as much? You will recall the frantic flag- waving and bugle-blowing by Conoco last summer, when it was threatened with a hostile takeover by Canadian interests.

And what do you further suppose the atmosphere here would be if the federal government in Washington were trying to cope, not only with the foreign ownership issue, but, simultaneously, with several separatist movements as well? Mr. Trudeau wants to move toward a national constitution that would substantially increase federal powers. Eight of the 10 provincial governments are fighting him. The Supreme Court told him last week that he technically has the legal power to proceed with the constitution in the federal parliament--in which he controls a majority. But the court went on to say that all of Canada's tradition and political practice warn him not to try it in the face of wide opposition among the provincial governments.

Neither good will nor good sense oblige Americans to approve every detail of the Canadian policy on foreign investment. But it is useful for Americans to keep in mind that, for the Trudeau government, the central issue isn't oil or dollars, but a future constitution and national unity.