SHOULD A MEXICAN AMERICAN be appointed ambassador to Mexico, as national Hispanic representatives urge? The question has been shelved, at least for the time being, by the decision to keep the current ambassador, former Wisconsin governor Patrick Lucey, in place. But since the question will surely come up again, it seems worth saying now that the post is too important to be treated as the special preserve of one ethnic group, even the group soon to be the country's largest minority. This is doubly so at a moment when the majority is finally beginning to comprehend the true nationwide American stake in Mexico.

No country is more important to the United States in terms of across-the-board, across-the-border impact on people's lives. Immigration is a huge and explosive phenomenon. Mexican energy reserves will make that country progressively more important to the American economy. Trade is large and growing and likely to become politically more abrasive unless it is spared mutual protectionist pressures. Borderland coexistence is a central fact of daily life for millions of Americans. The proximity of Mexico, the sieve-like character of the border, the traffic in people and goods, the collision of sovereignties and ideologies: The management of these elements requires not so much the special sensitivity a Hispanic American ambassador might bring as the concentration of the whole U.S. government.

The manysidedness of this relationship and its high domestic political content have led the administration to look for a new way of managing it. The State Department now intends to set up a special interagency coordinator just for Mexican-American affairs. The idea is to fill the post with a politically savvy person with access to the president. Some such experiment makes sense. At least within the government, a consensus has formed that Mexico cannot be treated like just another Latin or middle-ranking country: It's too big, too close, too important. In some matters, such as immigration, a special relationship must be formed; the legislation the administration is preparing is the crucial item here. In other matters, such as energy, a relationship must be defined that meets Mexico's need to be treated as a global equal; here the item to be watched is commerce in Mexican natural gas, a disaster area of recent policy.

As it happens, both Mexico and the United States are currently led by politicians interested in opening up and deepening the two countries' ties. That makes the moment rare and potentially fruitful. Politically and bureaucratically, it is a good time to sharpen the American focus on Mexico.