He was speaking at the National Press Club shortly before an unprecedented live television encounter with a representative of the Ulster Unionist Party.
Mr Adams suggested that the Unionists in the province had resisted engaging with Sinn Fein because of a sense of fear that peace talks would lead to their being cut off by the British government. 'The bewilderment of the Unionists at this time is because they feel a sense of betrayal,' he said.
He made the suggestion only hours before taking part late last night in a live television debate on CNN's Larry King Live between himself and Ken Maginnis, the Ulster Unionist MP for Fermanagh and South Tyrone.
It was to be the first such encounter between Mr Adams and any senior Unionist figure broadcast on television.
Raising the South African analogy on a day when Washington was playing host to President Nelson Mandela, Mr Adams suggested that only a figure like Mr de Klerk would be able to persuade the Unionists to put aside their fears and enter negotiations.
'I think that what is required from the British government is a De Klerk to move the whole situation forward and to encourage and persuade the Unionists that their future rests with the rest of the people of the island of Ireland,' Mr Adams said. He added: 'Some of the Unionist fears are totally and absolutely irrational.'
Mr Adams later held brief talks with senior members of the Clinton administration on the peace process. Because of a pledge by the administration not to receive the Sinn Fein leader in the White House, the meeting was held a mile away in the State Department. Today he travels to San Francisco and Los Angeles.