Mexican emigration: safety valve or brain drain?

The growing flow of Mexicans into the United States represents a ''safety valve'' for Mexico's whopping unemployment problem. Right?

Traditional wisdom would have it so. But there is evidence that the flow actually may not be such a boon.

In fact, new studies of the issue indicate the migration could become a source of potential social trouble for Mexico, for these reasons:

* Those going to the US tend to be more productive and better educated than those who remain, so the flow is something of a brain drain. Although the evidence is still sketchy, the migrants average four years of schooling, while similar young people remaining in Mexico average 3.1 years.

* The flow of migrants to the US is now more heavily from the cities than the countryside, and those who take their places in the cities, such as Mexico City and Guadalajara, are less skilled. The result is that jobs are being scaled down or replaced by machines - and if the migrants return, they won't find the same jobs.

* While the migrants are supposed to be sending home between $1 billion and $ 1.5 billion annually, these remittances may not be so high, and the money appears to be wasted by many of the recipients.

These are ''adverse consequences (of the migration) that should cause Mexico concern,'' says Dr. Allen Newman, professor of economics and finance at the University of New Orleans, speaking here at a conference on Mexico and the US in the 1980s. The meeting was cosponsored by Tulane University and the International Trade Mart here.

Although not all observers are so negative about the consequences of the flow on Mexico, a reassessment of the issue is being called for.

The exact number of Mexicans going the US yearly is hard to ascertain because so many of them are undocumented. But speakers at the meeting suggested that it ranges between 500,000 and 2 million yearly.

Many come for short periods, seeking temporary work, and then return home. The flow is larger than any similar immigrant tide in Europe or elsewhere. But in the view of many of the speakers it is the worst sort of flow since it is ''uncontrolled.''

Can it be controlled? Most observers think not. Edwin Chauvin, district director of the Immigration and Naturalization Service in New Orleans, said, ''It has proven impossible to seal the border.''

He and others suggested that the best possible solution now would be to go along with the Reagan administration's ''guest worker'' program and then seek to impose punitive measures on those employers in the US who employ Mexican ''illegals.''

Dr. Newman doubts that the Reagan program will work effectively. Its proposal to regularize 50,000 entries yearly ''is a drop in the bucket,'' and he adds that he is not particularly optimistic about ''any program getting through Congress.''

But even with approval of such programs, the tide is likely to continue until Mexico finds solutions to its employment problem.

At the moment, with Mexico's population soaring at a 3 percent increase yearly, about 850,000 new jobs are needed to take care of young Mexicans coming on the job market annually. Mexico is creating only about one-third of that total.

In the US, the immigrant flow results in part because of a vacuum. ''The undocumented are here,'' says Dr. Newman, ''because they fill a need.''