The young officer crouched on a steep hill above this small town near the Honduran border. He had just returned from a week-long patrol against guerrillas in the area.

"They were really entrenched in those hills over there," he said, pointing down to scrub-covered hills west of the town.

"We began right over there and chased them all the way to the border," he explained, sweeping his arm slowly toward the rugged mountains of Honduras, less than five miles away.

The hills around here, he concluded, were now "cleared out."

Five days later, a combined Army-civil militia column was ambushed in those same low hills. Newspaper reports said government units suffered more than 20 casualties. An Army spokesman confirmed that four of his men were killed.

The heaviest fighting now is in Morazan Province in the east, a province that had been swept by government troops last November. A government offensive there is reported to be sputtering.

The commander of Chalatenango Province in the north, long a guerrilla stronghold, said his region had been quiet for the last month. But there are three major guerrilla bases, each with about 500 troops and 1,000 members of their families, in the hills to the northwest and northeast.

The commander, a lieutenant colonel, said he has attacked the strongholds, each time finding them abandoned by the time his men arrived. He assumes the guerrillas have since returned.

He has not conducted sweeps lately -- he cannot afford to. "I've sent a lot of men over to Morazan," he explained.

If an Army outpost is attacked at night, "we don't go out to help," he said. "I would lose 20 men in an ambush trying to save 10."

This is a textbook guerrilla war. There are no battle lines. The government controls the cities. The guerrillas roam freely in the countryside, especially at night, in an area possibly covering a fourth of the country.

Government troops destroy and collect basic grain crops, such as corn and beans, to deny the guerrillas food. The guerrillas burn cash crops -- sugar and coffee -- to deprive the government of export income.

Recently the fighting has been a see-saw war of attrition. The guerrillas, after their failed "final offensive" in January, are reportedly regrouping and training recruits, avoiding government troops and staging small hit-and-run attacks on government forces. U.S. officials say the guerrillas are still receiving arms from supporters abroad, although it is not clear in what quantities.

U.S. officials estimate there may be up to 4,000 trained, well-armed guerrillas, backed up by perhaps 5,000 hapahazardly armed, barely trained irregulars.

Facing them is a Salvadoran Army of about 9,000 men, backed up by an equal number of government security forces: the National Guard with about 4,000 men, the National Police, with about 3,000 men and the Treasury Police.

In addition, as U.S. supplies come in, the Army is issuing cast-off arms and ammunition to thousands of peasants in "civil defense committees," a new version of the right-wing terrorist group called ORDEN, which allegedly was disbanded when the military government of Gen. Humberto Romero was ousted by a group of civilian and military reformers in October 1979. When asked, the "civil defense" men say that they are, in fact, members of ORDEN.

The Salvadoran high command exudes confidence these days, in large part because of the equipment arriving from the United States -- the first installments of a more than $25 million package headed this way.

And they are confident because they held off the guerrillas in January without that aid, as Defense Minister Jose Guillermo Garcia recently boasted, "without a single cartridge from the United States."

Now they are receiving far more than cartridges. Many troops are already equipped with U.S.-made M16 automatice rifles. Tons of ammunition, machine guns, mortars, helicopters and logistics and communication equipment are either here or en route.The buildup reportedly will give the military a firepower and mobility it never had before.

Then there are the controversial 56 U.S. military advisers here to teach the Salvadorans how to use and maintain their new gear. The advisers include 15 Green Berets who will help form and train a new 1,000-man rapid deployment force designed to go after large confrontations of guerrillas.

U.S. officials insist the advisers -- U.S. spokesmen prefer to call them "instructors" -- will no go into combat. So far the advisers seem to have stayed in the main garrisons or heavily fortified command posts or at the military airport seven miles east of the capital. U.S. officials say they are aware that because of opposition in the United States to a military role in El Salvador they can ill-afford to have advisers killed in combat.

At a farewell ceremony last weekend, Col. Eldon Cummings, outgoing head of the U.S. Military Group here, praised the assembled Salvadoran high command. They had made a "good start," he told them. "But you all know that the struggle is not over yet."

When asked how long it might take to defeat the guerrillas, Cummings said, "at least one year, maybe longer."

Privately, some Western observers and well-informed Salvadorans predict a much longer struggle.

"All they [the armed forces] can do now is push them [the guerrillas] around," said one foreign analyst. Another, noting that the Army was still fighting in Morasan after a major offensive there last fall, said the armed forces "just seemed to be going over the same gound."

"The way the Army is doing it," said a Salvadoren former top military official, "it could go on forever." He complained that the government troops were not "going out after the guerrillas," preferring for the most part to stay near the main garrisons and protect the cities.

But the present plan, according to some well-informed foreign sources, does not call for wiping out the guerrillas, something many believe cannot be done without massive Army losses.

The plan, according to those sources, is to keep pushing the guerrillas around, to keep them from launching major strikes, making them use up precious supplies and ammunition. Unless they are resupplied, the guerrillas, according to the plan, will eventually be diminished as a fighting force.

The official Salvadoran and U.S. view is that the guerrillas have lost much support in the last few months. These sources emphasize that the "mass insurrections" the guerrillas called for in the cities during the "final offensive" never materialized.

But that loss of support, foreign analysts concede, is not necessarily because most of the people no longer want the guerrillas to win, but because they are afraid of the government.

"The people," one foreign observer said, "are simply terrorized."

Still, Salvadoran field commanders -- and some foreign analysts -- believe the guerrills appear to be having trouble getting new recruits. And the guerrillas, who used to depend on contributions of supplies and money for their cause, may be resorting to "war taxes" collected forcibly.

A schoolteacher in Sesuntepeque 50 miles northeast of the capital San Salvador, said the guerrillas once enjoyed considerable support, especially last fall, before the "final offensive."

"Everyone was for the Front [the Democratic Revolutionary Front, an umbrella organization of leftist and moderate groups] at that time," the teacher said, "but it's different now."

When asked why the left was losing support, he said some people were upset by some of the guerrillas' random terrorist attacks.

"But more than anything, it was the repression, the heavy repression, and the failure of the offensive," he said grimly. "After all, we Salvadorens are not suicidal."

For the moment, one well-informed source concluded, "the government seems to be winning -- but not by much. The peasant is no fool, he wants to go with a winner."

A major guerrilla victory, such as the capture of a provincial capital, could change public sentiment, and this war, overnight.