Mexico wonders: mistake to back left in Salvador?

Mexico is having second thoughts about its policy on El Salvador. Its recognition of leftist guerrillas there has come in for some blistering criticism from other Latin American countries.

And the policy has been rebuffed in a number of circles at home: the business community, the military, and, interestingly, the government itself.

The Franco-Mexican declaration calling El Salvador's leftist guerrillas "a representative political force" has become an embarrassment.Many Mexicans say it was a blunder to be laid on the doorstep of Foreign Minister jorge Castaneda de la Rosa.

The governments of venezuela and colombia, together with Argentina's military leadership have takesn sharp issue with Mixico on this declaration. Venezuela is quietly trying to get both Mexico and France to change their stance, arguing that recognition is interference in El Salvador's internal affairs.

Four countries receiving Mexican oil at reduced prices -- Costa rica, the Dominican Republic, Guatemala, and Honduras -- have also publicly criticized Mexico's position.

"We may have lost a lot of the prestige we had won over the past several years for our careful hemisphere and economic overtures," says a leading Mexican diplomat.

Such views are not limited to Mexico's diplomatic corps throughout Latin America, but are mirrored at home as well.

The joint declaration was issued at the very moment some government officials were beginning to express concern about the Salvadoran guerrillas and their cause.

Indeed, many mexicans say, the declaration, coming just weeks before Miguel de la Madrid Hurtado was named as Mexico's nest president, may prove the last hurrah fro Foreigh Minister Castaneda and incumbent President Jose Lopez Portillo -- on the international front, at least.

The political focus now shifts to Mr. de la Mardid's pro-forma election campaign and away from the incumbent, a lame duck until the end of his term Dec. 1, 1982.

At the same time, officials around Mr. de la Madrid are understood to be extremely unhappy with the support given the Salvadoran guerrillas and are doing what they can to clip Mr. castaneda's wings. It is unlikely he will be forced out of the Cabinet, but his power clearly has been weakened.

Behind home-front concern over Mexico's El Salvador connection is fear that Salvadoran political and economic chaos will spread to other Central American countries. Such a spread could seriously threaten Mexico's southern flank, which borders on Guatemala -- and Mexico's bif oil fields are close to that border.

Mexico has recently beefed up its military garrisons along that border and begun a careful watch for Guatemalans and others entering southern Mexico's rain forests. Just last week, border patrols sent more than 2,000 Guatemalans back across the border.

While most of them were just looking for jobs in more prosperous Mexico, there were hints that some of them may have been leftist guerrillas using Mexico as a haven from Guatemalan military units in a search-and-kill mission near the border.

Mexico's interest in supporting the Sandinistas in Nicaragua is also beginning to flag.

Although cheap oil and other aid will continue flowing to Nicaragua, the amounts will likely be reduced.