Identification of at least five bodies found in an abandoned mine shaft as those of persons seized following the 1973 coup has dealt another blow to the credibility of the military government.

President Augusto Pinochet's junta has insisted that it had no responsibility for the hundreds of persons listed as missing. It charged that the issue was raised as part of an international communist campaign to undercut the government that overthrew Marxist Salvador Allende.

Human rights groups inside and outside Chile have long insisted that the missing Allende supporters were executed as part of a deliberate policy to eliminate the political left.

As with the assassination of Orlando Letelier, it looks as if another of the Pinochet government's darkest and most sensitive secrets is being exposed.

At the same time, it is a measure of the relaxation of press self-censorship and an increasingly assertive and independent judiciary that the abuses that occurred here after the coup are now coming to light.

While there are some 650 missing persons, in the case of the five positively identified from the mine shaft, there is virtually no question that they were last seen alive in the custody of police. The government has offered no explanation of their fate.

Even government supporters now acknowledge that the 14 skeletons found in a mining shaft in Lonquen are probably all persons executed without tral for political activities.

On Oct. 7, 1973, Sergio Maureira Lillo and his four sons, Segundo, Jose, Sergio and Rodolfo, were taken from their peasant hut 18 miles west of Santiago.

The five men, according to testimony long on file with the Roman Catholic Church in Chile and with the United Nations, were arrested by three members of the national police known to the Maureira family.

The five men were then taken to the National Stadium in Santiago, where political prisoners were held after the coup. Neither Sergio Maureira nor any of his four sons was seen alive or heard from again.

Residents of Lonquen, another small village about 30 miles west of Santiago. have said they remember hearing shots and vehicles coming and going one night after curfew in early 1974.

What appear to be bullet holes are also said to be visible in an abandoned house near the mine shaft where the skeletons were found three months ago.

According to the Catholic Church's human rights organization in Chile, the skeletons were discovered after a secret police agent confessed knowledge of the incident to a priest. Some clothing was found at the site.

Since late November, Adolfo Banados Cuadra, a judge assigned to Santiago's appellate court, has been assembling facts to present to the court.

Olga Adriana Maureira was shown the clothing and the skeletons and was able to identify a jacket and pair of pants as having belonged to her father. She also identified other clothing as that of her four missing brothers, she later told reporters from Santiago newspapers.

Banados has acknowledged publicly identification of the bodies.

Little is known of the political sympathies of the younger members of the family but Sergio Maureira Lillo was an unsuccessful candidate for alderman on his town council during the years before Allende's fall. He ran for a small non-Marxist party of the left.

Whether Banados will be able to complete his investigation remains to be seen. He has indicated that he will call the police identified by the family to testify.

The government so far has refused to cooperate with judicial investigations of missing persons.

Even if the government does decide to cooperate, the chances of anyone being tried are small. Pinochet declared an amnesty last year that covered crimes during the first 4 1/2 years after the coup.