Robert Frost's neighbor stubbornly maintained that "good fences make good neighbors." But Frost wasn't convinced. And neither am I. Some fences make bad blood, and we are building that kind of fence along the Rio Grande.

It is symptomatic of the way U.S. policy toward Mexico is managed that the contract for the lengthening and strengthening of the fence on the Texas-Mexican border was announced by the U.S. Immigration and Naturalization Service without any advance notice to our ambassador in Mexico City. What proved to be a traumatic blow to neighborly feelings, one which dominated the Mexican news for many days, was tossed into the diplomatic thicket as carelessly as a child might toss a match into a pile of leaves.

Similarly, a year ago the Department of Energy intervened at the last minute to put a bureaucratic road-block in the way of the purchase of Mexican natural gas by U.S. energy companies. The gas deal had been negotiated at length between Pemex, the official Mexican petroleum agency, and private U.S. companies. The Mexican government's longrange energy plan had been based on the sale and export of natural gas and the alternative consumption of more oil at home. Economic and other considerations had been calculated and the construction of the pipeline to the U.S. border had begun. The whole fabric of this agreement was rent when an abrupt, unilateral ruling was issued by the Department of Energy in Washington on the stated ground of objection to price. In that one decision, years of a positive, mutually beneficial relationship with the Mexicans were jeopardized. The president of Mexico, one of the friendliest in recent history, was left, by his own description, "hanging by his paint brush" when we knocked over the ladder. And Mexicans generally have been given reason to wonder whether our vaunted "free-enterprise" system is a reality or a myth.

So whether it is building fences on the Rio Grande, or buying gas or oil from south of the border, it is time to get our act together.

In the first place we have to ask whether building fences is an effective answer to the problem of illegal immigration from Latin America into the United States. It may be easier and cheaper to help by giving would-be migrants a reason to stay home.

It is estimated that about 800,000 Mexican workers move silently and invisibly across the border every year. Some work a while and return to their homes and families. Some remain in the United States. The facts are not well known and are hard to prove. No one knows what the cumulative illegal immigration now amounts to, but it is surely many millions.

The U.S. government's response to the situation has been feeble and ineffective. We have neither welcomed these visitors as a supplement to our work force and tried to regularize their activities nor have we been able to deny them entry or jobs.

Governmental indecision is reinforced by the attitude of organized labor. The unions are fearful that any move to regulate and control the alien workers will also legalize them, so they have opposed any move in that direction. At the same time, labor has taken no interest in developing other soultions.

The subject is a painful one for the Mexican government, which does not discuss it very freely. The government exposes its sensitivity quietly for several reasons. Any brutal action to expel resident aliens and to repel migrant workers would be an ethnic insult with serious political impact. On the practical side, the Mexicans working in the United States are a significant source of dollars and one that Mexico cannot afford to lose just now. So governmental enthusiasm for keeping people home cannot be counted on as a deterrent.

In the past, problems such as these have been allowed to fester because the effort and cost of finding solutions was greater than the potential benefit. Now that is all changed as her economy grows and as she discovers some of the earth's largest reservoirs of energy -- both gas and oil.

Let us look at the changes. The ties that bind Mexico and the United States are becoming increasingly important; we must not ignore them. Oil is only one of the more obvious. As Mexico adds to its oil production, it could become a secure source of energy for the United States. At present, we take the bulk of Mexico's 500,000 barrels per day in oil exports. As these exports increase, Mexican oil will pose a very attractive alternative to our dependence on imported Middle East oil. Events in Iran only underscore the dangers of this dependence on distant sources of energy.

It is estimated that Mexico could provide as much as 30 percent of our import needs by 1985. Even if Mexican oil does not flow directly to the United States, the very existence of a major new petroleum source entering the market cannot help but have a positive effect on world energy supplies and prices.

Oil is not, however, the only issue that binds our two nations together.

Mexico is the fifth largest trading partner of the United States. In 1977, $9 billion in goods and services were exchanged by our two countries. The Mexican government is attempting to stimulate and diversify Mexico's export capabilities. The U.S. market is an important factor in this effort. Problems arise, however, to the extent that Mexican exports compete with U.S. domestic production. But these are problems that can be worked on and eased.

I do not have answers to all the questions pending between our two nations. But answers must be found, and to find them the United States must devote far more attention in the future to its critical Mexican relationship than it has in the past.

I welcome the administration's current review of U.S./Mexican relations. I believe it vital, however, that we develop a mechanism for coordinating our governemtn's dealings with Mexico. The time has long passed when each separate department of the U.S. government could afford the luxury of its own individual, uncoordinated Mexican foreign policy. When the Department of Energy rejects a gas deal with Mexico, the negative repercussions across the range of our relations with Mexico could hobble us for years to come.

On the question of illegal immigration, I want to reiterate what I said following my visit to Mexico in 1977. Rather than simply applying unilateral regulations designed only to stem and reverse the tide of illegal immigrants, the United States should consider ways to encourage the government of Mexico to initiate large-scale labor-intensive development programs in Mexico's rural areas, where most of the migrants originate. It seems clear that the government of Mexico will need significan outside help if it is to address the task of absorption and resettlement without incurring massive social and political unrest. Relief measures that could be considered include the exemption of the products of a Mexican rural development-resettlement plan, from U.S. tariffs or other trade restrictions for a given period. While this idea could become unwieldy in practice (how to discriminate between "new development" products and others for example), efforts should be made to find and establish concrete economic incentives for Mexicans to remain within their own development areas.

On this increasingly difficult issue, Mexican/U.S. relations are at a threshhold. There are no easy solutions, indeed there may be only partial solutions. But one thing is certain: The problem cannot be satisfactorily resolved by unilateral measures. Legislation, not reinforced by strong and effective programs to provide relief for persons who may be returned across the border, will create a grave threat to the stability of Mexico -- a stability that is of vital concern to our own country.