Puerta has said he was not interested in the presidency

Eve Rimoldi, constitutional law expert

As head of the country's Senate, Mr Puerta was next in line to succeed after Mr de la Rua's departure.

A relative political unknown, Mr Puerta, who is in his early 50s, arrives on the scene at the height of the country's most severe political and economic crisis for years.

He would be allowed to complete Mr de la Rua's term in office, which was due to end on 10 December, 2003, but may go to the polls sooner.

"Puerta has said he was not interested in the presidency and the constitution would allow early elections to be called," said Argentine constitutional law expert Eve Rimoldi.

Although outwardly unassuming in character, Mr Puerta is an experienced politician with more popular appeal than many of Argentina's other older mistrusted political leaders.

Mr Puerta was twice governor of Argentina's poor northern Misiones Province between 1991 and 1999.

He served in the Chamber of Deputies for two years before winning a seat in the Senate, where he was subsequently elected chairman.

A self-made millionaire, Mr Puerta is unmarried with two teenage children.

He made his fortune, reputed to be about $6m, from trading traditional Argentine herbal tea.