Insurgency : Salvador Rebels Lose Support in Latest Offensive : The guerrillas say they want to ‘punish the armed forces’ and reduce the military.

Supported by new antiaircraft weapons and taking advantage of the army’s static defensive tactics, Salvador’s guerrilla movement has raised the country’s civil war to its highest level in a year.

Since Nov. 20, the leftist guerrillas have shot down a government jet fighter and a C-47 gunship with surface-to-air missiles and destroyed at least one military helicopter with ground fire. The missiles are a troublesome development for the army because air power has been its biggest advantage in the 10-year civil war.

From the rebel point of view, “the timing is excellent at this stage,” according to a military source.

“You already have an armed force stretched very thin, and now many of the country’s agricultural crops are about ready for harvest,” the source said, pointing out that the army is being used to protect plantations and processing plants.

“One of the problems of the army is the protection of the economic infrastructure. . . . There are at least 50 strategic sites that have to be guarded,” he said.

In spite of the tactical opportunities, the current rebel offensive perplexes many diplomats and military experts and seems to have alienated even further the already faded international support once enjoyed by the Farabundo Marti National Liberation Front (FMLN), as the guerrillas call themselves.

“I can’t figure out what they are doing,” said one Western diplomat about the offensive that has taken at least 220 lives--75 government soldiers, 121 guerrillas and 24 civilians--and left about 400 people wounded. Not since the November, 1989, offensive have casualties been so high.

The FMLN calls the offensive an effort “to punish the armed forces” and says it is also aimed at forcing the government to negotiate a peace agreement that includes a sizable reduction of the military and the dismissal and punishment of officers accused of human rights violations.

The guerrillas also argue that the increased attacks on dams and other electrical power sources, which have left as much as two-thirds of the country without electricity, “are a repudiation of the economic policy that has brought misery to our country.”

However, random interviews with ordinary citizens in San Salvador and in the countryside indicate little sympathy for such a position.

“My boss told me to stay home today because we don’t have any power at the factory. When I don’t work, I don’t get paid,” said Carlos Ramos. When asked whom he blamed, Ramos responded: “It’s the FMLN. They don’t have to do that. It only hurts people like me.”

Reporters also found people puzzled and embittered by the fighting in their neighborhoods, particularly when they were not allowed to leave their homes to escape the fighting.

“The civilian casualties are really hurting them,” said one Western diplomat whose government strongly backs the Salvadoran regime of President Alfredo Cristiani.

While this view might fairly be questioned as biased, it was endorsed by a Latin American diplomat whose government in the past was sympathetic to the FMLN.

“I suppose there is something to the argument that the FMLN has to increase attacks once in a while to keep the pressure on the government,” this diplomat said. “But . . . attacking targets in areas where civilians are bound to get hurt is a great mistake.”

The new fighting has also brought public condemnation from every other Central American country and the United Nations, as well as private criticism from former allies in Mexico, Spain and Venezuela.

Another puzzling element in the guerrilla timing concerns U.N.-sponsored peace negotiations. After the failure of several rounds of direct talks to achieve significant progress, U.N. mediator Alvaro DeSoto has privately circulated a draft agreement widely seen as favorable to the FMLN and which has been described in optimistic terms by Cristiani.

“The only explanation I can think of,” said a European diplomat with close FMLN contacts, “is that radical elements (within the FMLN) can’t bring themselves to accept any agreement not entirely on their own terms, even though DeSoto has given them much of what they want.”

Agreeing with this view is the military source.

“They have lots of factions they have to keep together,” he said. “And in times of stress they gravitate toward the most militant.”