Ms Sarney is ahead in presidential polls

The split between the parties ends Mr Cardoso's congressional majority and could complicate his final eight months in office.

But analysts said the two parties were likely to remain close, at least until it becomes clear which of their candidates stands the best chance of defeating the left-wing presidential hopeful, Luiz Inacio Lula da Silva, in October's poll.

The row blew up last week after federal police raided a company belonging to Roseana Sarney, PFL candidate and member of a poweful northern Brazilian clan.

Corruption probe

Hundreds of thousands of dollars and documents found in the raid have been used to suggest that the company was involved in a high-profile corruption scandal.

Ms Sarney claimed the raid was politically motivated and demanded the PFL withdraw its backing from the government.

She said Mr Cardoso's allies wanted to discredit her to boost the chances of Jose Serra, the candidate from the president's Social Democrats (PSDB).

The PFL is the biggest party in the lower house of Congress, giving it an effective block on some government bills.

Some analysts said party leaders only wanted a symbolic break, to allow Ms Sarney a clear run for the first round of the presidential poll.

The PFL's significance

Largest party in lower house Controls Brazil's poor north Coalition member for seven years Holds the vice presidency

Whichever party's candidate was ahead after the first round could then become a joint candidate and run against Mr da Silva, the other strong challenger.

The BBC's correspondent in Brazil, Tom Gibb, says the row marks the start of what promises to be an acrimonious presidential election campaign to succeed Mr Cardoso, who is not allowed to run for a third term.

Following the PFL decision, its three ministers will resign and PFL officials at other levels of government are also likely to step down.

But vice president and PFL member Marco Maciel said he intended to remain in office.