Two congressmen resigned their posts today in a spreading bribery scandal that could involve a member of President Fernando Henrique Cardoso's government, an administration that has prided itself on scrupulous integrity.

The scandal broke last week when Brazil's largest newspaper, Folha de Sao Paulo, published what it identified as transcripts of taped phone conversations between two members of the Chamber of Deputies and a third man in which the legislators discuss taking bribes to vote for a constitutional amendment that would permit mayors, state governors and the president to run for reelection.

While the scandal is unlikely to block enactment of the amendment -- it was passed by the Chamber in January and the Senate tonight, and must be approved by the Senate again -- it could sully Cardoso's reputation for personal honesty, even though he is not accused of involvement in any payoffs. "The scratch on Cardoso is small, but voters are likely to remember this in the future," said Brazilian political consultant Alexandre Barros.

The congressmen -- Ronivon Santiago and Joao Maia, both members of the government-allied Liberal Front Party from the Amazon state of Acre -- were quoted by the paper as saying that they and three other lawmakers from the state received $187,000 each to vote for the amendment.

Subsequent published transcripts quoted Maia as saying he believed the money had come from Sergio Roberto Vieira da Motta, the minister of communications and a longtime friend and business partner of Cardoso.

"Nobody wants to believe {Cardoso} is involved, but the fact that he's a close friend of Motta is worrisome," said Paul Steele, an analyst with Banco Geral do Comercio in Sao Paulo. "Had it been any other minister . . . no one would have bothered much."

Motta, nicknamed "Bulldozer" because of his abrupt manner, angrily denied Maia's assertions, calling them "baseless" and "repugnant." Cardoso has stuck by Motta but called for a thorough investigation of the apparent payoffs, saying they "cannot be swept under the rug."

The Chamber of Deputies, in which Cardoso's allies hold a majority, created a special panel last week to investigate the affair but gave it only limited powers and just a week to report its findings. As part of its probe, the panel commissioned a study of the telephone tapes by forensic scientists, who verified the tapes' authenticity and identified the voices on them as those of Santiago and Maia, the Reuter news agency reported.

The scandal apparently came as a surprise for Cardoso, 65, who took office in 1995. During decades of public life -- as an academic driven into exile by the 1964-85 military dictatorship, a senator and a cabinet member -- Cardoso had a reputation for incorruptibility.