Salvadoran guerrillas get upper hand -- with Cuban aid?

The bitter struggle in El Salvador between government forces and leftist guerrillas is suddenly going badly for the government. Battlefield reports indicate that the guerrillas, who hold sizable portions of the countryside, are now increasing their control over much of the western part of the country -- and that the Salvadoran Army has been unable in recent weeks to dislodge the guerrillas or to make any significant inroads against them.

The battlefield reverses for the Salvadoran military are sounding alarm bells in Washington.

The are also hints that Cuban advisers may be on the scene assisting the guerrillas. It has been assumed all along that the guerrillas were receiving military equipment from Cuba, and the Cubans have indirectly substantiated this assumption.

Now, however, if Cuban advisers are on the scene, the whole struggle takes on a new coloration.

The Reagan administration is deeply worried about the ability of President Jose Napoleon Duarte's government to hold on to power. The United States, which has been the Salvadoran government's major support for the past two years, has supplied its own advisers to the Salvadoran military as well as sending in sizable quantities of military equipment.

The guerrilla resurgence is a sharp reversal of the situation six months ago, when it appeared that a stalemate in the five-year struggle was developing. Neither side appeared able to defeat the other.

Indeed, it was felt in some quarters that President Duarte's shaky military-civilian coalition government might be able to get its act together enough to win support from El Salvador's beleaguered populace and even to begin making inroads against the guerrillas.

US military assistance, which was resumed in the twilight days of the Carter administration and has continued under President Reagan, was expected to help improve President Duarte's situation.

Ironically, however, President Duarte's most encouraging days were in January during the height of a guerrilla offensive that eventually fizzled. That was before renewed US aid began arriving in significant quantities to have an effect on the battlefield.

Since then, as the struggle has worn on without any major breakthrough for either side, Salvadoran military units have been accused of an increasing wave of violence against civilians, many of them suspected guerrilla sympathizers. This situation has brought down considerable worldwide criticism on the Duarte government.

President Duarte's refusal to enter into a negotiated settlement with the guerrillas' political arm has also been sharply criticized.

The surprise Mexican and French decision in late August to recognize two leftist guerrilla groups as a "representative political force" is widely viewed as an effort to get the Duarte government to the negotiating table.

But the Mexican-French action has clearly cheered the guerrillas, although the recognition was roundly criticized by the governments of Colombia and Venezuela, which accuse Mexico and France of interfering in Salvadoran internal affairs.

It was noted in Mexico City, however, that the joint Mexican-French document is not as strong a statement of support as the Salvadoran guerrillas would like.

The document does not recognize that a "state of belligerency" exists in El Salvador, something that Mexico and several other Latin American governments recognized in the case of Nicaragua.

That recognition gave significant legitimacy to the Sandinista guerrillas during the revolution there.

In addition, Mexico continues to recognize the Duarte government and continues to supply it with some of its petroleum.

It is also not overlooked that Mexico, like the US, is deeply worried that the Salvadoran struggle will spill over into Guatemala, where leftist guerrillas are already locked in a serious battle with the government.

Many Mexicans are deeply worried about the consequences for them of a worsening situation in Guatemala, with which they share a border.

While the Mexicans do feel that the guerrillas are likely to emerge the winners in El Salvador eventually, some observers think the Mexican government would prefer to have them do their winning at negotiation table rather than on the battlefield.