Two Argentines who escaped imprisonment last year offered detailed testimony yesterday on secret detention camps where, they charged, more than 250 fellow detainees were "transferred" -- a euphemism for murdered -- at the hands of the armed forces and federal police.

The two men, Horacio Cid de la Paz, 22, and Oscar Gonzalez, 29, appeared at a London press conference under the auspices of Amnesty International, which circulated their written testimony worldwide.

Martin Ennals, secretary general of the organization that won the 1977 Nobel Peace Prize for its work on behalf of political prisoners, said the testimony was published after Amnesty was able "to corroborate many of the details."

The escapees, who spent 15 months in captivity, offered significant new information on the phenomenon of "disappearances" in Argentina. Amnesty has previously charged that more than 15,000 Argentines are missing as a result of kidnapings by security or paramilitary groups since the military coup of 1976.

Gonzalez and Cid estimated that about 800 prisoners were held in the five secret detention centers in and around Buenos Aires where one or both of them were held. They said they saw numerous government officials at those camps, including an Army corps commander.

While they described vividly the torture that they said was routinely applied to them and the others, the two said they eventually obtained better treatment by joining work details in the camps.

This, too, gave them their chance to escape, which they refused to detail, saying they sought to protect others still in Argentina. Cid admitted membership in the leftist Montonero guerrilla movement and Gonzalez described himself as a political activist.Both denied having taken part in any guerrilla activity.

The two said their assignment to work details gave them wide contacts with fellow prisoners and permitted them to keep account of numerous prisoners who, first allowed to think they would be freed, were then "transferred."

"Immediately after our escape, we used all possible means to try to find out if any of the comrades transferred had shown any signs of being alive. The result was negative," they said in joint testimony.