The Argentine Army high command announced today that Maria Consuelo Castano de Gonzalez and her three small daughters, whose disappearance was reported last week to the Inter-American Commission on Human Rights, had been detained because Gonzalez was a terrorist who had recently returned clandestinely to Argentina.

The Army communique said Gonzalez had been picked up by Army intelligence units on the evening of Sept. 13 as part of an investigation that led to the deaths of two well-known Montonero leaders on Wednesday.

The two terrorists, Horacio Mendizabel and Armando Croatto, were killed in a shootout with police in a supermarket not far from the apartment where the Gonzalez family lived.

According to police sources, one of the terrorists attempted to throw a grenade at security police but shot himself in the stomach when the grenade failed to explode. The other terrorist pulled a gun and fired at police before he was killed. The army communique said two policemen were injured during the shootout.

The communique said that Gonzalez's three daughters, aged 5, 4 and 3, had been taken to a "special facility" while their mother remained in custody. No mention was made of the woman's husband, Regino Adolfo Gonzalez, who was also reported missing by members of his family.

It was understood here that Regino Gonzalez also returned recently to Argentina under an assumed name after living for several years in Mexico, where many Montoneros have gathered in exile.

The disappearance of the Gonzalez family during the visit of the Inter-American Human Rights Commission here received widespread publicity after the commission formally expressed its concern about the incident to the government.

The Army said today it had detained Maria Gonzalez, whose code name was given as "Chela," to prevent her from telling Mendizabal and Croatto that security units were close on their trail.

Argentina's military junta was also reported to be working on another case today about which the commission expressed concern during its visit. That case invovled Jacobo Timerman, a newspaper publisher whose release from house arrest was ordered earlier this week by Argentina's Supreme Court.

There were rumors, published in newspapers here, that the junta would allow Timerman to leave Argentina next week. Rumors of Timerman's imminent release have been published before, however.

Like Gonzalez family, Timerman also "disappeared" before Argentine security forces admitted that he was in their custody.

Human rights groups estimate that between 8,000 and 20,000 Argentines have disappeared since the current military government began its "dirty war" against terrorism three years ago.