Fifteen thousand people marched on the Casa Rosada presidential palace tonight, demanding that the military government reveal the fate of the 6,000 to 15,000 people who "disappeared" during repression of leftist guerrillas and other dissidents in the 1970s.

It was Argentina's largest human rights demonstration since the military overthrew the constitutional government in March 1976.

The march was organized by eight rights groups, including the Mothers of the Plaza de Mayo who have mounted an often lonely vigil for years to protest the abduction and presumed death of their children. The groups handed over nearly a quarter of a million signatures on petitions asking the government to give a full accounting of the missing.

A delegation consisting of Hebe Bonafini, head of the mothers' group, Nobel Peace prize winner Adolfo Perez Esquivel, two Catholic bishops and a handful of other rights activists was admitted into the palace along with two shopping carts full of the petitions. The group was not, however, received by any government officials.

Bishop Jaime F. de Nevares of Neuquen said, "There was a porter to receive us but no one responsible, so we didn't want to leave the petitions . . . . The best thing they could have done is receive the signatures. That would be in their favor, but politically they've made a big mistake."

No arrests or injuries were reported during the demonstration. However, a police car that tried to divide the marchers' column by driving through it was forced to retreat under a hail of stones.

The petition calls for the immediate return of more than 100 children allegedly abducted by the security forces, and for the release of political prisoners. The petition also rejects the idea of an amnesty for those found guilty of illegal repression.

It has been widely reported here that the government plans to announce such an amnesty next week saying "excesses" are to be considered as acts of service and should be pardoned.

The marchers walked more than a mile through downtown Buenos Aires, chanting antigovernment slogans and urging pedestrians caught in the rush-hour traffic to join them. "It's going to end--this habit of killing," the crowd sang. "We want them alive, just as you took them," they chanted, as people watched from their balconies, many cheering them on.

Scores of marchers carried signs bearing the photos of missing persons with a legend giving the name and date of abduction. Contingents demanding answers about the hundreds of Chileans, Paraguayans and Uruguayans who also disappeared in Argentina mixed among the crowd.

"You see this kid?" a protester said to a bystander while pointing to a poster of a very young child. "What did he do to disappear?"