The president's trip to Mexico this week is a haunted mission: Late additions to the passenger list included the ghost of oil past, the shah, and the ghost of oil future, the ayatollah.

Certainly their spiritual presence has given all the more emphasis to the petroleum side of things, and to the American effort to stimulate what has lately become known as oil proliferation. What the Carter trip has already stimulated is an extraordinary enthusiasm about Mexican oil. The excitement has been most clearly expressed in the call for a "hemispheric energy policy," in which Mexican petroleum is to be a key element.

The phrase is rather grand. Unfortunately, no one has yet been able to delineate what it means. More important, it is highly misleading -- both about Mexican oil prospects themselves and about how that petroleum relates to the Western world's acute energy predicament.

While the phrase has a progessive sound in the United States, it can have quite the opposite effect on Mexicans (and Canadians, as well). For it suggests that the United States regards their oil and gas as its own, and wants to decide the disposition of these hydrocarbons. Any such schemes are fodder for extreme nationalists in those countries and are likely to be viewed with suspicion even by moderates, who see in it a kind of good neighborly oil grab.

The administration has recognized this more clearly than some of its critics.

"We're dealing with a very sensitive relationship," said one American official who is traveling with Carter. "After all, Mexico was the first developing country to nationalize its own oil industry."

The rate of development of oil in itself is a very sensitive issue. Generally, oil producers are taking a second breath now, for the lesson of Iran is all too obvious. A slower and less traumatic development is a safer course, and that is Mexico's choice.

American interests in these circumstances are not so hard to identify -- to see the development proceed at a rate that does not undermine Mexican society. This, after all, is also the Mexican interest. Thus, a more sensible approach for the United States is one of less grand posturing but more practical and less intrusive assistance. In other words, we should be as forthcoming in terms of capital, technology and markets -- in helping the Mexicans to develop their own oil industry -- as they want.

An obvious place to begin is with the importing of Mexican natural gas, which got caught up in the long battle over domestic U.S. natural-gas prices. That tedious battle is fortunately over, and it should be possible in the next few months to quickly resolve this question in a manner highly favorable to all concerned. The United States should be accommodating and understanding, not combative. As important, our self-defeating ban on the export of Alaskan oil might be laid aside through a three-way swap involving the United States, Mexico and Japan.

That step should not, however, be confused with the idea that it is better that Mexican oil go to the United States instead of, say, France. Actually, it does not matter where the Mexican oil goes, so long as it goes on the world market, and more rapid development of production may well be facilitated politically in Mexico if the United States is only one among several buyers.

But it is exactly when one looks at Mexican oil in the context of the world market that the pessimism sets in. For this enthusiasm and the talk of oil proliferation obscure a harsher reality. Many Americans are looking to Mexican oil as a way to reduce substantially our dependence on the Persian Gulf and as a harbinger for the possibilities of oil proliferation. Especially now, with Iran not only out of oil, but politically out of control. Unfortunately, desire and need are running far ahead of facts, with the result that the Mexican potential, at least on the basis of what is known so far, has been subject to great exaggeration, leading to a belief -- stated ad nauseum this week -- that another Saudi Arabia sits on our doorstep.

The experience around the world since 1973 suggests that an exceedingly tight and precarious oil market -- not the glut of recent legend -- is the likely pattern for the future. A North Seasized oil province, or two Alaskas, must be found every year to avoid a peak of production around the turn of the century. One Mexico in the 1970s only pushes the date back a few years.

And that brings us back to the ghosts traveling with the president. Nothing has happened to reduce in the next few years the dependence on Middle Eastern production, with the consequent costs as dangers all too obvious today.

Mexican oil is not going to have much effect for a number of years. Exports will not exceed 2 million barrels a day until the latter part of the 1980s. Meanwhile, production in Iran is unlikely to be more than 60 percent of the old level. In other words, the matter can be stated starkly: It will take six or seven years for Mexican exports to reach a level where they will make up for the oil that the regime change in Iran permanently removed from the world market in a matter of weeks. Chatter about "another Saudi Arabia" provides a pleasant diversion from a staggering problem, but hardly does much to concentrate our minds on what we are up against right now.