Joya Ancha Abajo, El Salvador — A dozen guerrillas from the elite Rafael Arce Ableh Brigade crouch in a small cornfield to avoid detection by a Salvadorean Army plane. The drone of the United States-built O-2A reconnaissance plane keeps them from setting up ambushes and artillery. They appear relaxed, shifting their knapsacks and M-16s.
The rebels are confident that they have the upper hand in the countryside in the civil war - despite a summer lull in guerrilla activity that US and Salvadorean military sources had interpreted as a loss of guerrilla strength. In a new offensive, guerrillas have made more than 50 strikes on towns and villages since early September.
The guerrillas in this field, most of whom have fought for at least two years , say they see a recent change in the war.
''The Army sent out small patrols to engage our units, but these received heavy casualties,'' says one guerrilla who identifies himself as Modesto. ''(So) now they have decided to bomb towns they suspect we occupy.''
As we speak, the 0-2A plane circles nearby cornfields and small towns. The twin-engine craft stayed on after the other members of an Army contingent of helicopters and planes left after a morning bombing and strafing raid.
Guerrillas here assert that the increased bombing and air attacks by the Salvadorean armed forces demonstrate the Army's increasing impotence on the ground.
''More and more,'' says one guerrilla, ''this is becoming an air war. It is a sign of the Army's desperation.''
The Army may not be desperate, but it does appear to be falling back into its previous role as a reactive force, say many close observers. For example, the Army units sent out to reoccupy Tenancingo and Jucuapa after they had fallen to guerrillas, never entered the towns until the rebels had withdrawn.
''The Army has always used helicopters and planes, but not to the extent they are utilizing them now,'' says one veteran of the four-year conflict, ''and (previously) they rarely bombed population centers. Now they aim rockets and bombs directly at residential dwellings.''
Guerrillas claim that since the bombing by the Salvadorean Air Force of Tenancingo on Sept. 25, several smaller population centers have come under air attack.
The Tenancingo bombing by US A-37-B ''Dragonfly'' jet fighter-bombers left close to 50 civilian dead, according to relief workers and eyewitnesses. The fighter-bomber, used heavily in Vietnam, also demolished several houses in the town.
On the rebel side, each new offensive shows an increase in guerrilla firepower and strength. In the current offensive, the rebel forces - known collectively as the Farabundo Marti National Liberation Front (FMLN) - have begun to use heavy artillery. The rebels say they are leading up to large-scale military assaults.
These insurgent troops claim to have captured 280 soldiers since the offensive began. Most of these soldiers were released to the Red Cross although guerrillas claim that some have volunteered to join the fight against the Army.
The guerrillas say they have captured 350 automatic weapons, some mortars, and four trucks in the past month. They also claim to have taken stores of ammunition from overrun government outposts.
They maneuver large numbers of their troops and equipment into position with trucks. The FMLN forces are also operating larger groups than at any other time during the war.
Guerrillas leader Joaquin Villalobos, who is generally considered the overall military commander, has reportedly been reorganizing the five-member FMLN into bigger units. These units have been confronting groups of several hundred soldiers. In a recent radio broadcast, on the guerrilla clandestine ''Radio Venceramos,'' Villalobos said that the string of attacks in the current offensive will ''at any moment reach with greater force into the capital and provincial capitals.''
After recent Army passed in this region, several houses near this dirt road between Santa Elena and Jucuapa bear the marks of strafing and bombing attacks. One house, destroyed by a rocket from an 0-2A, retains the smell of burnt gunpowder. The rocket casing lies outside the demolished structure with its lot number listed in English.
These bombings have caused a flood of refugees into Santa Elena. Most houses and small towns in the area have been abandoned.
The plane from which the guerrillas are hiding fires two rockets at targets in the distance and drops to follow the road in its effort to search out guerrilla units.