AMONG WASHINGTON'S current preoccupations, the Mexican fishing treaties draw hardly a semi-shrug. But it's worth observing that this country is now engaged in quarrels over fishing rights in both oceans, with both its immediate neighbors. Canada and Mexico make, with justification, the same charge -- that the United States won't make up its mind, and refuses to bring a growing list of ugly little disputes to any conclusion at all. Why? Because some of the American fishermen object.

The Mexicans have decided to cancel the treaties that permit American commercial fishermen to operate in Mexican waters, and Mexicans to fish off New England. The immediate stakes are not large. But it's a gesture of exasperation at the stalemated negotiations over the much more significant issue of tuna fishing in the Pacific. For some years, large and well-equipped American boats have ranged freely far down the coast. Now the Mexicans have decided to use some of their new oil wealth to go into deep-sea fishing, and they are asserting jurisdiction over their coastal waters out to a limit of 200 miles. The Americans continue to work those waters, the Mexicans occasionally seize their boats, and the friction is growing. It's the kind of dispute that diplomats are supposed to resolve routinely.

The Canadian case is even more egregious. It concerns the rich fishing grounds off Newfoundland and New England, and here the diplomats did their work well. Two treaties have been signed establishing boundary arbitration and joint management of the fisheries. That was an eminently rational settlement. Unfortunately, ratification has been blocked for nearly two years by several New England senators. The American fishermen think -- correctly -- that under any sensible system of management they would be limited to catches smaller than their present ones. The result is that the treaties are not in force, and this continent's greatest fishing grounds continue to be severely overexploited, to the profit of today's fishermen and the cost of tomorrow's.

These fishing disputes reflect, of course, the tightening worldwide competition for food supplies. But in both Mexico and Canada, they are also taking on a broad political significance. There the American failure to respond is increasingly considered a demonstration of intent to trespass. At the least, by giving the fishermen's lobbies a veto over national policy, the United States has relegated its neighbors' rights to a notably low priority. Perhaps the American performance has been affected recently by the sensitivities of an election year. But that year is over. It's time to settle the fishing quarrels.