A guerrilla-backed local government in this leftist stronghold supervises farming, passes out medicines, sells sugar and cigarettes and enforces a law code including prohibitions against treason, public drunkenness and cutting down shade trees.

The self-described "popular" government has the twin purposes of providing goods and services for guerrillas and peasants here and of showing that the rebels can administer a territory in defiance of the national government.

There is little to govern in these impoverished, war-scarred mountains in the eastern end of Chalatenango province near the Honduran border. Evaristo Lopez, 39, the president of the "subregional" government, presides over a zone that is roughly equal in size to Washington, D.C.

No usable roads penetrate his domain, as the three that exist are mined or have become impassable due to lack of repair. Distances are measured in walking time on the narrow trails that connect half-deserted villages and totally empty ghost towns. Nearly six years of Army and Air Force attacks have left most of the mud houses in ruins overgrown with vegetation, and the population is estimated at about 3,000, of whom half are small children. Three years ago it was 10,000.

Nevertheless, this area boasts the country's most developed "alternative" governing structure. The guerrilla army based here, the Popular Liberation Forces, has placed more emphasis on building a popular base than have the other rebel forces in the umbrella Farabundo Marti National Liberation Front.

Only in two other Popular Liberation Forces strongholds have the rebels even tried to establish an administrative apparatus as sophisticated as the one here. Those areas are in Chalatenango's other "subregional" zone in the mountains northwest of here, and on the slopes of the San Vicente Volcano to the east.

The most important task of the "popular local power," as the government is called, appears to be supervision of agriculture. Local rebel officials help draw up plans for how much corn, beans and rice are to be grown, and they then ensure that everybody has enough seed and fertilizer. They also ensure that a certain quantity of resources is set aside to grow food for the guerrillas, who are too busy fighting to till the fields.

The target for dividing up the harvest is to give 8 percent of the crop to the guerrillas and leave 92 percent in the hands of the peasants who did the work, according to local officials. There did not appear to be any resistance to this arrangement, as the only people willing to live in this area are strongly committed to the rebels.

Health care is the government's second priority. The area boasts two mobile "hospitals," each of which consists of a doctor, a nurse and several backpacks full of basic medicines and medical equipment. The hospitals have to be able to move in a hurry, as the armed forces seem to make a point of trying to capture guerrilla health facilities. The military has often announced the capture of rebel clinics.

Dr. "Francisco," who runs one of the hospitals, performs surgery on a crude, wooden table that resembles an ironing board. Instruments are sterilized in water boiled over a wood fire in an adjoining, half-destroyed building.

In addition, most inhabited towns have a simple dispensary where young women hand out aspirin, antiparasite pills and other medicines, and pull teeth and diagnose ailments. They receive 10-day training courses taught by a local revolutionary government health official, whose lessons focus on politics as well as sanitation.

"Malaria is transmitted by mosquitoes, which tend to breed in puddles and stagnant water. The bourgeois government has permitted this to happen, because factory owners and landowners don't want to pay taxes to keep the environment clean," lecturer Leon Abrigo told a recent class.

The local government also runs five "popular stores" that sell basic foods and consumer items at a maximum profit of 10 percent. There used to be nine such stores, but four have closed because of the difficulty of transporting goods past armed forces roadblocks without arousing suspicion. Cooperatives have been formed to sew clothes, fish and make shoes.

Finally, the local government has drawn up a legal code dividing crimes into three categories: very serious, serious and light. Anyone can accuse anyone else of a crime, and guilt is determined by cross-examination and achievement of a consensus by all present at the hearing.

"The simplicity of the laws responds to the situation. People know each other here," Javier Orellano, 30, the government's secretary of legal affairs, said.

Two persons have been executed under the code, both for armed robbery in early 1984. Someone found guilty of a "light" crime, such as drunkenness, might be required to patch the roof of a house damaged in an air attack. A peasant who cut down a shade tree without permission was forced to plant five new ones.

The local government junta is made up of a president and vice president, and secretaries of legal affairs, health and the combined department of education and social welfare. These five officials were elected from a slate of 10 last December, but there was no campaigning and people reportedly voted mostly on the basis of which individuals they trusted. In addition, the outgoing junta made nominations that bore considerable weight.

"Elections here are qualitatively different from those of the enemy. The candidates do not run to serve their individual interests or to get rich, but only to help the people," said Erik Mejivar, 35, a former accountant who joined the rebels in May 1984 and helps the local government keep its books.

In theory, the local governments operate independently of the guerrilla force. But as Maria Serrano, a former local president and now an adviser to the junta, explained: "We have a vanguard, and it gives us ideas. It's not that the vanguard tells us what to do, but it makes suggestions and we discuss them."