A court petition filed today calls for Argentine authorities to identify some 400 people it says are buried in a paupers' wing of a cemetery here. The plea follows exhumation at the cemetery of a body said to have been identified as that of a youth abducted by security forces in 1976.

The petition, filed by six parents of "disappeared" persons, asked that Judge Hugo Gandara investigate the identity of the people in the unmarked graves at the Grand Bourg Cemetery near San Martin, about 15 miles northwest of the capital and one mile from Argentina's largest Army installation.

The petition says that the graves may contain some of the estimated 5,000 or more persons missing and believed killed by security forces in their campaign against leftist guerrillas in the mid-1970s. The ruling military has made no public accounting of the disappearances.

"We are asking that the government clarify this situation and the cases of all those people who are still missing," said Augusto Conte MacDonell, one of the parents, at a news conference tonight. Conte MacDonell's son, Augusto, has been missing since July 7, 1976.

The petitioners, members of a group called the Families of Persons Disappeared or Detained for Political Reasons, asked that Gandara impound all records and relevant cemetery documents, that the grounds be put under guard and that testimony be taken from cemetery workers and area residents.

"We are concerned that the cemetery could be altered," said Ruth Penette de Gutierrez, one of the petition signers, at the headquarters of the Permanent Assembly on Human Rights in downtown Buenos Aires. "We have called this news conference in part to make sure that evidence does not disappear."

The petitioners cited the case of a youth, whose name they did not reveal, who they said was dragged from his bed six years ago by security agents and subsequently listed as a "disappeared person" until a judge told his parents in 1981 that the young person was dead. The body, later located through court documents, was buried underneath the bodies of three others at the cemetery, they said.

The petitioners said the circumstances and timing of the kidnaping and disappearance resembled the disappearances of their children.

"We're acting as parents whose children could be buried like the victim already found and we're asking that an investigation take place," said Emilio Mignone, also a petitioner and head of the Center for Legal and Social Studies. A daughter of Mignone is among the missing.

"President Reynaldo Bignone has said we should direct our grievances through the court system. This is an opportunity for the judges appointed by the military to show they are truly independent," said Mignone.

The petitioners said that since the cemetery was established in 1976, an estimated 400 cadavers have been buried in 88 common graves in an area known as the "no-name zone." Each of the graves held five or more cardboard caskets placed one on top of the other, they said.

"These burials were made at night and the cadavers were transported in vehicles belonging to security forces, causing the workers to work at night in groups of six or seven," the petitioners allege. The petition asked the judge to determine if officials broke any laws.