At least 1,500 persons arrested in Chile since the military takeover of 1973 have "disappeared," Amnesty International said yesterday at press conference held here and in New York to publicize the plight of political prisoners worldwide.

The London-based organization said it has "complete documentation" on 500 prisoners whom the Chilean authorities disclaim ever having taken into custody. It daid the overall figure of 1,500 is "a conservative estimate."

Chilean lawyer Jose Zalaquett, who was arrested and then exiled after working with prisoners for an ecumenical church committee, said the disappearances are Chile's attempt "to avoid the pressure of world opinion by giving the impression that theare are not more arrests."

Zalaquett testified last May before a U.S. congressional hearing, then putting the number of prisoners who have disappered at 1,000.

Chile released or exiled more than 300 prisoners late last year and Zalaquett's successor group in Chile has reported that virtually no arrests or disappearances have occured within recent weeks.

The government contends that those disappearing in the past have gone underground or fled the country. Relavies in many cases have presented extensive evidence of the victimes having been taken into custody.

Amnesty International officials said press conferences will be held in Washington and London next week to focus on the situation of prisoners in Argentina.