The exodus from Cardoso's eight-year government is taking place because Brazilian rules oblige holders of executive office to leave their posts six months ahead of a vote if they are running for office, political experts have said.

The resignations will help define the closely watched presidential election, with a number of potential candidates set to confirm whether they are running.

The April 6 deadline, which applies to all candidates running in the October presidential, congressional and state elections, is also expected to prompt state governors to step down in droves as they run for other elected posts.

``This is an important date, as you will see which ministers and governors will resign to run for office,'' said political analyst David Fleischer.

Cardoso is expected to announce replacements for the ministers, who will mainly be senior civil servants who have worked in the ministries, during this week, officials said.

Among the senior government officials to resign this week to meet the deadline are the Vice President, the budget, justice, communications, labour and national integration ministers and Cardoso's Chief-of-Staff.

The most-closely watched decision may be that of Maranhao State Gov. Roseana Sarney, who is running for President for the centre-right Liberal Front Party, but whose bid has been tarnished by a police raid on a company she owns which turned up 1.34 million reais ($570,000) in unexplained cash.

Another four senior officials, including the energy and environment ministers, already left the government in recent weeks over election wrangles with Cardoso's Brazilian Social Democratic Party, or PSDB.

Cardoso's former Health Minister, Jose Serra, resigned earlier this year to launch his campaign for the presidency for the PSDB. Cardoso cannot stand again in the election.

However, key government officials such as Finance Minister Pedro Malan, Agriculture Minister Marcus Vinicius Pratini de Moraes and Foreign Minister Celso Lafer are set to stay.