A real opportunity will be lost if the Senate Finance Committee votes against the creation of a North American free trade area with Canada. The question is whether to let the Canadian negotiations go forward under the special procedure that trade agreements require. In the Senate an accumulation of irritations and suspicions now threatens to end the talks on a free trade area before they really get started.

Why? There are many layers of reasons. First of all, several senators -- notably the committee's chairman, Bob Packwood of Oregon -- fear the impact of Canadian competition on the American lumber industry. But that's just the beginning. Some of the senators suspect that, under pressure to get an agreement, the negotiators would be tempted to avoid the issues that promise to be most important in the future -- trade in services, for example, and intellectual property rights. There is a longstanding quarrel over Canadian treatment of American patents. The senators want more assurance than they've received that this kind of thing will be included.

More broadly, most of the committee is exasperated with President Reagan's single-minded pressure for free trade and his dismissal of the consequences for jobs. The administration has refused to deal with the committee on trade issues, the senators say, and now they will -- perhaps -- refuse to deal with it. This committee is the same one that is also struggling, not very successfully, with the tax reform bill and the requirements that Mr. Reagan has imposed on it. There is no direct connection among these different concerns. But in the committee's revolt over Canadian trade you can distinctly hear the echoes of senators' accusations, in regard to tax reform and budget deficits, that the president is refusing to carry his proper responsibilities.

As for the trade negotiations themselves, there's certainly no guarantee that they will succeed. Canada's prime minister, Brian Mulroney, has a reputation for edging away from the kind of abrasive political combat that the prospect of free trade is generating on his side of the border. Sen. Packwood's lumbermen are not the only people in North American who would like to leave things as they are.

And yet there's an opportunity. The flow of trade between Canada and the United States is the greatest between any two countries. A trade agreement offers each of them the advantages of expanded markets. With their similar economies and legal systems, these two ought to be able to achieve a model of a fair and foresighted trading regime. These negotiations could set precedents to guide future agreements with Europe and Japan. That's not a prospect to be discarded lightly.