Last fall, Defense Minister Jose Guillermo Garcia insisted that prolonged guerrilla occupation of El Salvador's northeastern corner was meaningless because the rugged back country had little economic or military value.

This month, Garcia stationed the U.S.-trained Ramon Belloso Battalion in the same area with orders to police as much territory as possible, including the town of Perquin, which had been in rebel hands since October and was retaken at the beginning of February in a major military operation.

The shift, following a string of guerrilla successes, marked a step away from strategy urged on Salvadoran officers by their American advisers, who repeatedly have emphasized protection of economic targets rather than control of such isolated towns and villages near the Honduran border.

Garcia's new determination to control northern Morazan province reflects concern over the strength demonstrated by rebel forces in their recent push southward from pockets they had controlled unopposed since fall. Although they drew back after two days of a large government offensive, the guerrillas for the first time in the 3-year-old civil war had NEWS ANALYSIS held ground, even for a short time, against a conventional Army attack.

Their increased ability seemed to confirm what critics of the U.S.-promoted strategy had been saying. This was that writing off the remote rebel strongholds on the grounds that they had no value of their own gave the guerrillas time and territory to organize their forces, while at the same time handing them the political advantage of ruling Salvadoran territory.

The confirmation was particularly vivid in the Feb. 6 capture of Berlin and attacks on nearby bridges across the Lempa River on the coastal road linking San Salvador with the rich agricultural areas of Usulatan province.

Guerrilla forces driving down from the long-occupied Morazan pocket showed such strength that Garcia responded with an operation that concentrated more than 5,000 troops, including all three of his U.S.-trained battalions, in northern Morazan. As that battle raged, other guerrillas struck at Berlin, more than 50 miles to the southwest in the heart of the economically important region that U.S. advisers had insisted was the most critical of the war.

In mounting such a large operation and exposing himself to the trap at Berlin, Garcia also was disregarding U.S. advisers. The American officers have for months been warning that large-scale sweeps are questionable unless followed up by constant small-unit patrols to scour the countryside for any reemerging guerrilla presence.

A military expert said Garcia's decision to post the elite Belloso brigade in northern Morazan could prove effective only if the troops stay in the area and mount frequent patrols to keep it free of rebel infiltration.

Past experience suggests this is unlikely. After a large sweep through guerrilla redoubts in Chalatenango province late last year, Garcia pledged to villagers that soldiers would remain to protect them, then allowed his forces to withdraw within 10 days. As a result, the mountain villages resumed their role as a guerrilla rear area.

Long-term guerrilla occupation of remote areas has facilitated temporary movement by rebel forces into more important towns as well. They have been able to fade away into the border strongholds when government troops pull near to attack.

A band of guerrillas took over La Palma in Chalatenango province earlier this month, for example. They harangued the local population with revolutionary appeals, marched about the town square, held a dance and slipped back into the safe hillsides before government troops responded.

There is no way to measure accurately the effect of such visits on Salvadoran villagers. Guerrilla leaders win a few recruits at most and spray-paint the walls with slogans. But most Salvadorans hold their political sentiments within, bending with the guerrillas or the Army according to who is on the ground.

Guerrilla leaders appear aware of the public relations value of their appearances, however, and the rebels who took over La Palma gladly escorted foreign reporters around town and invited them to the dance. Hearing of this, another group of guerrillas telephoned a news agency office in San Salvador to suggest that reporters also might want to visit the newly occupied town of Sociedad on the other side of the country.

The U.S. ambassador to the United Nations, Jeane Kirkpatrick, said during a recent visit here that such image-making is part of the strategy for guerrilla war.

"It proceeds through military means, and through propaganda means, and through the media, too, if I may say so," she told correspondents. "It proceeds through images as well as through violence and the manipulation of images as well as through the manipulation of violence, and at any given point there is some kind of combination of these that is creating some kind of impression."