Santa Clara, El Salvador — ''Please stand at attention,'' a rebel leader calls to several dozen Salvadoreans slurping homemade popsicles here in Santa Clara's central plaza. The villagers, who have been ordered to the plaza by several guerrillas toting automatic rifles, dutifully respond. They do not join in, however, as the rebels lustily sing an off-key rendition of a revolutionary song.
''Nicaragua has won,'' a rebel leader shouts when the song is finished. His companions rejoin, ''and El Salvador will win.''
This gathering in the plaza is being held to honor the five-year anniversary of the Sandinista revolution in neighboring Nicaragua.
But the main message is a lambasting of the new government of Salvador President Jose Napoleon Duarte. The rebels' speeches appear to recognize that Mr. Duarte's election has scored political points for the government. And the question implicit in the their remarks is: Is the the guerrillas' base of popular support diminishing?
Several times during the meeting in the plaza the speakers question the new President's credibility and power. They portray him as a puppet of United States President Ronald Reagan.
''A few of the people have been fooled by Duarte,'' says a rebel commander of the Popular Liberation Forces.
''Although all the policies in El Salvador come from Reagan, Duarte has been able to pass for a democratic representative,'' says one rebel commander, whose nom de guerre is Matilde.
''(Duarte) has promised peace, which is what people want, but we are going to see him fail. The workers, believing there is more liberty, will begin to strike for fair wages and Duarte will respond with repression, at which point he will be exposed as a tool of the military in the US.''
The rebels in this central province of San Vicente appear strong militarily.
''The guerrillas are better armed and move in larger groups than they did a year ago,'' says Santa Clara's Christian Democratic mayor, Carlos Antonio Aguilar.
But the guerrillas know, perhaps as well or better than anyone here, that political losses in an insurgent war can be as damaging as military defeats.
''It is clear that Duarte cannot bring a solution to El Salvador,'' says a rebel whose nom de guerre is Fredi. ''Before Duarte took power he said he would negotiate with the (guerrilla front) to reach a political solution to the Salvadorean problem. Now he says he won't negotiate with armed groups.''
''We are not going to drop our guns before we reach a solution,'' he says. ''Duarte is not going to provide what he promises to the Salvadorean people.''
''The enemy says we are destroying the country,'' Matilde says defensively, leaning his G-3 automatic rifle against a low concrete wall. ''We are not destroying the country. We are destroying the old, corrupt system to build something new.''
The last rebel orator reminds his audience that when Duarte was in power in the El Salvador from January 1980 to March 1982, Archbishop Oscar Arnulfo Romero , several popular Roman Catholic priests, four United States churchwomen, as well as four Dutch journalists were assassinated.
The rebels also criticized Duarte's trip to Europe last week as an effort to get ''more bombs and more weapons to intensify the war.''
In recent weeks the rebels have intensified a forced recruitment drive in this area, although local officials contend that no youths have been taken from Santa Clara.
The rebels halted all traffic on the major highways in this part of the country for six days last week.
Three weeks ago they overran the country's largest hydroelectric dam, Cerron Grande.
The guerrillas contend they killed upward of 200 soldiers during the attack, took more than 100 prisoners, destroyed equipment, and captured some 400 M-16 rifles. During the Santa Clara meeting, however, the guerrillas say they captured 500 soldiers.
''The stopping of the traffic,'' says the unit commander whose nom de guerre is Louis, ''was calculated to target those military vehicles that had to travel on the roads, hurt the economy, and demonstrate our military power both internally and to the international community.''
The cessation of traffic was unpopular with some Santa Clara residents, but the forced recruitment, they say, is untenable.
El Salvador's Army has presented to press what it claims are documents captured from a rebel base in another area. These documents order local rebel commanders to shoot deserters.
Residents in Santa Rosa and several smaller towns in the area who have had young men return after being taken by the guerrillas denied the charges, although are embittered by the new guerrilla policy.
''To say we take people violently'' says Louis, ''is wrong. We take youth in the same way the Army does, but we give them a choice.
''If they want to go back after a week with us, they may. Seventy-five percent ... decide to incorporate.''
After Santa Clara was overrun by the guerrillas on Sept. 25 last year, it has become increasingly isolated.
''There are few food deliveries and almost no transport to and and from the town,'' says Mayor Aguilar. ''I assume the Army wants to stop any supplies from reaching the guerrillas.''
The mayor says he has not been able to pay his four employees for the past six months and petitions to the government for assistance have been useless.
''I intend to close the mayor's office at the end of the month,'' he says.
The guerrillas, according to residents, have turned Santa Clara into a staging area for military forays and a depot for the acquisition of supplies.
''Our fear is that if all food and supplies are cut off the guerrillas will start to take what little we have,'' says one Santa Clara resident.
The guerrillas admit that they often lack sufficient food, but contend that this is not unusual for them.
''Our food situation is critical'' says Matilde, ''but this doesn't bother us. To be hungry only gives us more courage to fight.''
The conclusion of the town meeting is meant to be a display of revolutionary solidarity. Town members are told to clench their left fists and raise them in the air.
The villagers oblige, holding their arms limply over their heads. In front of them stand the four guerrilla leaders, their muscles taut and their faces rigid. For several moments the two groups face each other in silence.
Finally one of the guerrillas says, ''You can lower your fists. Thank you.''