While guerrilla fighting units venture out daily from this rebel-held zone to war with government forces, commanders and ideologues behind the lines are fighting their own daily battles against the backwardness and isolation of the Salvadoran peasantry that forms the bulk of their army.

It is a problem the guerrillas share with their enemy, the Salvadoran military, as each side struggles not only to win the hearts and minds of the population, but to mold its recruits into an effective fighting force.

In the northeast zone of the country where the Farabundo Marti Liberation Front took this correspondent on a guided tour, motivation appears high. The peasants, banded together under rebel protection in support of the fighters, are organized for survival against the military. Even the elderly and infirm among the local peasants proudly proclaim themselves "guerrillas."

These peasants say they are fighting against government "repression," and their stories are punctuated by charges of military assassination and mass murder of civilians. Although no evidence has surfaced of similar massacres of noncombatant civilians by the guerrillas, the rebels have been accused of assassinating government officials, soldiers and sympathizers, as well as their families.

Aside from these controlled zones and quick, commando-style raids into towns and villages, the guerrillas have not attempted to "sweep" the military from regions it occupies. Many of the alleged government massacres have taken place during military attempts to rout the guerrillas from civilian-populated zones.

While the guerrillas' protective role seems to have been accepted by the peasants, acceptance of their ideology is not as clear.

The sophisticated Marxism expounded by the official guerrilla theorists seems far removed from the realities of life here. While ideological training figures as high as military drilling on the agenda of the commanders, potential peasant fighters being taught in four-week courses at a guerrilla "academy" here in the hills frequently need more instruction in the simplest ways of the world.

Orlando Rodriguez, a burly former dockworker who heads one of the academies visited, described a weighty program steeped in rhetoric, with classes on "bourgeois ideology" and "relations between the party and the Army."

In practice, the training program revealed the extreme backwardness, and the effects of decades of bitter poverty that are the despair of commanding officers in the government Army and the guerrilla forces alike.

"The relation between the party and the Army was included in the program because so many compas fighters thought that carrying a gun made them better than the production workers." Rodriquez explains.

"We also teach 'proletarian ideology.' This is necessary because the compas sometimes feel embarrassed that they have only one change of clothing and have to spend Sunday standing around in their shorts while they wash and dry their uniforms. We explain that we fight even in our shorts. Of course, all our instruction is difficult because only rarely does a compa know how to read. We don't have time to teach them, either."

Instead, the trainees learn how to use a latrine, how to wash their hands after using it, how to clean and take a weapon apart and other combat basics. Standing skinheaded in the courtyard of their adobe school/barracks, some barefoot, some in dilapidated boots, the trainees practiced what looked like extremely awkward shooting positions, then demonstrated "an assault on a barricade with diversionary tactics," as Rodriquez put it, looking very comical in their leafy camouflage.

According to "Javier," in charge of one of the military camps visited, the guerrillas are divided into squads of 10 to 11 men and platoons of two squads each. Every squad has a commander, a political director, a paramedic, a cook, and an administrator of supplies.

Above the platoon level Javier said there are only "areas," and "zones," whose size and number of personnel were unspecified. Above it all is a commander-in-chief for each of the five fronts into which the country has been divided, with his own comandancia general, or chief of staff. Each front, the guerrillas claim, has eight "control zones."

The government estimates the total number of guerrillas between 3,000 and 6,000.

In the area of the Morazan "control zone" visited by this reporter, the guerrillas were predominantly armed with automatic rifles, mostly U.S.-made M1s, but also West German G3s, U.S-made M16s, and Belgian FALs.

"Juan," who works in logistics, claims that the G3s and M16s were "recuperated" from government troops, and the other weapons were purchased on the international black market.

The U.S. and Salvadoran governments have charged, and presented allegedly captured rebel documents as proof, that the guerrillas are principally supplied by clandestine arms shipments from Cuba and Nicaragua. Although questions were raised by opponents of U.S. policy about the allegedly large quantity of weapons shipped, little doubt has been expressed, despite Nicaraguan denials, that the nearby Central American country has served as a conduit for some guerrilla supplies. Cuba, while not publicly offering details, has never denied its overall "support" for the Salvadoran rebels.

Juan denied that any arms came from Cuba or from Nicargua's Sandinistas. "We have taken extreme pain to avoid giving the United States any excuse to intervene directly in El Salvador. Nicaraguan and Cuban arms are easy to identify, and would provide that excuse. But for us there is an even more important reason: politically we are not innocent, and we know that accepting arms means accepting certain kinds of commitments. We don't want those kinds of ties in our future government."

This reporter did not accompany the guerrillas on any military operation, and had no independent way of verifying what kind of weapons are actually used in combat or in other zones. In the area visited, there seemed to be a great scarcity of weapons, as well as of clothing, medicine and food.

Before leaving on missions, a squad in one camp visited was seen trading weapons and boots with those who remained behind. Food rations here as elsewhere were invariably two tortillas and a small serving of beans, meat or broth at every meal. Those about to leave on a mission get slightly more. At most camps sweet coffee also is available in the morning and evening.

The paramedics devoted most of their attention to enforcing elementary hygiene in the camp, but had little medicine to work with. Many inhabitants interviewed in the control zone, both civilians and combatants, complained of some form of intestinal infection or skin disease.

The guerrillas maintain, with some credibility based on the extensive territory from which the government forces have not been able to dislodge them and a growing string of military victories, that they have had more success in gaining, motivating and training recruits than their opponents.

Part of their strategy, they said, includes taking government soldiers prisoner and attempting to disarm them both of their weapons and their loyalty to the Army.

"It is much better for us to have soldiers surrender than to die fighting," said "Melo," a grinning, dandyish youth who is in charge of defense for the northeastern front. "First of all, we want them to hand over their weapons, but most importantly, we want to create good relations for the future, when we will build our 'new type army' with combined guerrilla and government troops."

Five prisoners sat in a hot, bare, dusty courtyard bounded by a half-hearted attempt at a wire mesh fence. They sleep in an adjoining one-room adobe structure precisely like every other peasant house in the area. When questioned, they say they are doing what they do all day: "Waiting for the next meal."

Jose Alberto Martinez, 16, is the youngest. Like the others, he was recruited into the Army six months ago. Unlike the others, he is from Morazan, and has a brother fighting with the guerrillas. He can write enough to sign his name, he says.

Manuel Antonio Rosales was a subsergeant nurse in the Army for five years before he was captured with the others in a battle at the village of La Guacamaya last Dec. 29. His fellow prisoners are barely literate migrant workers, but Manuel is articulate and sophisticated. He is careful to say nothing that will displease his captors, but clearly has no sympathy for the guerrillas.

The others are much more candid. "We like the food here," Nelson Ernesto Orellana, 25, says. "A little meat, a little soup . . . . In the Army it was always rice, beans and spaghetti."

"And they the guerrillas didn't beat me," adds Guadalberto Campos, 18. "In our unit the officer didn't beat anyone, but in other units it's very frequent. I thought they would do that here too."

There appears to be no systematic attempt at winning over the prisoners to the rebel side. The guerrillas claim they have released most of their prisoners after a brief period and that a few have voluntarily joined their ranks.

None of the five interviewed had any intention of joining the guerrillas, but neither did they intend to rejoin their Army units. "We will have to go to another province to look for work, because the Army will kill us if they find us," said Manuel Antonio, the nurse. "We're not supposed to surrender. But none of us wants to fight again."