Border accord

The United States-Canadian border has to be one of the world's most remarkable political boundaries. Stretching across the North American continent for some 4,000 miles, the border is largely unpoliced. Thousands of cars stream back and forth daily. Tourism is commonplace. Most important, the combined trade in goods and services that crosses that border represents what is perhaps the largest two-way trade among any set of nations - certainly among any two neighboring countries.

All Canadians and US citizens have a clear stake in taking all possible steps to expand that trade. That both nations are now considering proposals to do just that is especially encouraging, given the acrimony over economic issues that has unfortunately marked political discourse between Ottawa and Washington in some recent years.

What is new in the whole trade equation is that the two countries are now exploring the idea of additional limited free trade.

Both nations have already worked out such an agreement for the auto industry. But now there is speculation that agreements might eventually be hammered out for such areas as clothing, textiles, and mass-transit equipment. For Canada in particular, such a move would represent a major political shift away from the Liberal government's efforts to boost trade with Europe while reducing trade with the United States.

Looking northward, some tariff walls have gradually been reduced. A number of Canadian firms have located operations in the US - partly to tap the large US market, partly because of concerns that the government of Prime Minister Trudeau is antibusiness.

Obviously, neither the US nor Canada is yet ready to embrace any notion of a ''North American accord.'' The Trudeau government remains strongly nationalistic. And the US - through television, films, magazines - continues to impose a heavy cultural influence on a nation seeking to define its own individuality.

Still, there is no reason why the two nations should not work out new trade agreements in as many areas as possible, as considered in a study paper prepared by the Canadian Senate and as now being discussed by the Canadian minister of external trade. Free trade pacts would spur economic growth on both sides of the border. For Canada, firms enlarging trade with the US could convert their manufacturing operations to longer production runs, thereby bringing down unit costs. For the US, multinational firms with plants in both nations could more efficiently allocate production schedules. In short, everyone would gain.