Wedged into a narrow sliver of beach between steep, barren mountains and the Pacific Ocean, this tiny fishing village is a natural prison.

Access to the rest of the world is by way of a rutted, one-lane dirt track that winds up the mountains, feeds into a tortuously narrow pass and cuts 30 miles across the northern Chilean desert to the nearest highway in the middle of nowhere.

Now a virtual ghost town with a population of only 60 persons, Pisagua's main claim to notoriety came during the late 1940s, when it was used as a concentration camp for hundreds of outlawed Chilean Communists.

Last week, Pisagua temporarily became an open-air prison again with the enforced presence of two members of the banned Christian Democratic Party accused of violating a government decree that prohibits politcal activity.

Economist Elias Sanchez and party youth leader Juan Claudio Reyes, both in their early 20s, were among 12 Christian Democrats arrested during a Jan. 13 government raid on a meeting in a downtown Santiago office.

By the next morning, the 12 - without trial and protesting their innocence - had been sentenced to indefinite banishment and transported to villages in the sparsely inhabited mountains some 1,200 miles north of the capital.

Sanchez and Reyes wound up in Pisagua.

"The first night we were here," said Reyes during a walk down Pisagua's main and only street, "fishermen sat with us for hours. They kept bringing us beers, and asking what we had done to get sent here."

"You must have voted 'No' in the referendum," the fishermen decided. "Or else you are subversives."

No one really seemed to care, however, what the charged was. The visitors, and the rare excitement they brought, were welcome.

Christian Democratic leaders labeled the banishments the first evidence of an anticipated crackdown on opposition activity following the Jan. 4 nationwide referendum which showed an overwhelming 75 percent of Chileans in favor of Gen. Augusto Pinochet's rightist dictatorship.

But having proved its point that such activity would not be tolerated, the government has since backed down somewhat.

A court acknowledged the government's right to banish citizens from any given province and send them off to another, but it ruled that the government could not force people exiled in this way to live in a particular town or city.

So the 12 Christian Democrats were brought out of their banishment villages last week and taken to Africa, a small oceanside oasis that is Chile's northernmost city.

Internal exile has long been written into Chilean law, and the Pinochet government has occasionally used it as punishment. The case of the 12, which included party Vice President Tomas Reyes, 63, and one woman, union leader Georgina Aceituna, was remarkable in its apparent attempt to send exiles to the most unhospitable places possible.

The day after their arrest, Juan Claudio Reyes and 51-year-old ex-congressman Andres Aylwin found themselves, by way of military aircraft and jeep, in Guallatiri, a spot on the map marking a three-family Indian settlement near the bolivian border.

Accessible only by means of a dirt track frequently washed out by rivers that alternately dry up completely and overflow onto the harsh terrain, Guallatiri is 15,000 feet above sea level and 170 miles from the nearest hospital or food stores in Arica. Temperatures in Guallatiri vary from below zero at night to broiling daytime heat.

There, among the Ilamas and adobe huts, they were left in summer clothes they were arrested in, without food, medicine or shelter. Like the other 10 Christian Democrats scattered in similar locations throughout the area, their only contact with the outside world was through the carabineros , federal police stationed in mountain outposts, with whom they had to sign in daily.

It was the carabineros , in most cases, who gave the 12 unauthorized aid in the form of blankets and medical attention.

"There was a great deal of sympathy," one of the prisoners said. "The carabineros feel that they, too, have been banished by being stationed up here."

Soon after his arrival in Guallatiri, Aylwin, suffering from the nausea and dizziness of severe altitude sickness, was taken down the mountain to another village.

Gradually, a few relatives made their way from Santiago to the village, with food, medicine, books and clothing. Jose Reyes, 52-year-old father of Juan Claudio, walked the last 25 miles up the mountain to reach his son when his hired car reached an uncrossable river.

He stayed there the better part of a week until the next vehicle arrived, carrying an International Red Cross doctor visiting the area at the request of sympathetic diplomats and Christian Democratic leaders.

The immediate result of the doctor's visit was the transfer of Juan Claudio Reyes and Sanchez, who was being held in another mountain village, to Pisagua. Both had been suffering from severe altitude problems.

Last weekend, follwoing the court decision and the physician's report describing the debilitated condition of those left in the mountains, the total lack of sanitary facilities and the possibility of permanent injury, all of 12 were rounded up and brought to Arica.

Their two-week ordeal over, they are now lodged in an Arica hotel - at their own expense - waiting for the government to determine the length of their sentences.