The president of the Zimbabwe opposition party, Movement for Democratic Change, and two of his colleagues go on trial Monday on treason charges. They are accused of planning to assassinate President Robert Mugabe.

The state claims that Morgan Tsvangirai and Welshman Ncube, president and secretary general of the Movement for Democratic Change, and parliament member Renson Gasela conspired to have the Zimbabwe leader killed just before presidential elections last March.

They are alleged to have tried to enlist a Canadian, Ari Ben Menashe, in a plot to stage a coup d'etat in which President Mugabe would be murdered. The state says it has secret tape recordings of meetings between Mr. Tsvangirai and Mr. Ben Menashe.

High treason in Zimbabwe carries the death penalty.

The defendants deny the charges and say their meetings with Mr. Ben Menashe took place because he had promised to be a lobbyist for them in the United States. They say they learned later that he was actually an employee of the Mugabe government and was under investigation for fraud in Canada and Africa.

Mr. Tsvangirai is the first politician in 22 years to seriously challenge Mr. Mugabe's hold on power. He lost an election last year, but most Western observers and parliamentarians from the Southern African Development Community say the poll was neither free nor fair.

The trial judge is Paddington Garwe, who assigned himself the case. He was promoted to his present position as Judge President of the High Court after Mr. Mugabe purged the judiciary of many senior and respected judges.

Representing Mr. Tsvangirai and the other defendants is South African lawyer George Bizos, a longtime attorney and friend of former South African President Nelson Mandela.