Managua, Nicaragua — Guerrilla forces in El Salvador have suffered a series of setbacks since January, rebel leaders here say. These leaders, who ask to remain unidentified, attribute the setback to:
* Reorganization of the government's military high command.
* A change in the government's military tactics.
* Increased United States reconnaissance flights.
The rebels say their own forced recruitment drive, which began in January, has lost them both international and domestic support. They say they will end forced recruitment. Over the past eight months, several hundred young men and boys were abducted and pressed into guerrilla fighting units.
''We do not renounce our right to recruit from the population, but we realize that our image has been damaged by the recruitment,'' says a leader of the Popular Liberation Forces, the largest guerrilla group. ''It is better to build the consciousness of the people to induce them to join us,'' he says.
January was a pivotal month in the civil war, rebel leaders say. Three command changes made shortly before January resulted in an improvement in the government's military performance, the rebels say. The changes put Col. Adolfo Onecifero Blandon in the position of chief of staff for the Army; Lt. Col. Miguel Antonio Mendez was named chief of the Army operations, and Lt. Col Domingo Monterrosa Barrios became head of the Third Brigade in San Miguel.
''With these command changes the troops, especially the Cozador battalions ( 350-man units designed for counterin- surgency warfare), have been forced into the field more often and with more effectiveness,'' says one rebel.
The some 40 Cozador battalions, along with stepped-up air attacks and US reconnaissance flights, are being used to keep guerrillas on the run and to deny rebels fixed bases of operations, rebels say.
Col. Joseph Springham, the former head of the US military mission here, spoke about this military objective during his farewell press conference in June.
''Basically, the strategy is to keep the subversives on the move,'' the Vietnam veteran said, ''so they can't mass, can't support themselves, can't do anything. Frankly, we've been pretty successful.''
Rebel leaders reluctantly agree.
''When one Cozador unit is pulled out, it is immediately replaced by another to keep the pressure on us,'' a rebel leader says. ''If the entire Army is converted into these counterinsurgency units, the government will have an increased military capacity which could cause us some problems.''
The rebels say that increased US reconnaissance flights - now conducted daily by Mohawk obervation planes and C-130s taking off from airstrips in Honduras and Panama - are hampering the rebels' ability to mobilize and operate.
''We have heard soldiers are wearing tags or buttons that the infrared sensors on the US planes detect,'' one rebel leader says, ''This would allow the military to distinguish between our concentration and their own. As it is now, we have to be very careful about massing in large numbers.''
Guerrillas also say the Army is using new field radios that distort voice transmissions, making it impossible for rebels to intercept Army communications.
''We need to capture a few of these special radios before we can understand what is being said,'' a rebel says.
Guerrillas here say that despite these difficulties, they can overcome the Army advancements.
''They lack the experience the guerrilla fighters have. When we face them in combat it is obvious that they do not want to put themselves in any danger.''