The diplomatic tangle between Venezuela, Argentina and the United States reached a new pitch on Monday when a jury in Miami convicted a wealthy Venezuelan businessman of acting as an ''unregistered agent'' of Venezuela on American soil.

The matter, known in Latin America as ''Suitcasegate,'' started last year with the discovery of a mysterious suitcase filled with $800,000 in cash at an airport here. But it has erupted into a scandal that has aggravated tensions between the United States and its neighbors to the south.

Franklin Dur? the businessman convicted Monday, was tried in Miami on charges of conspiring to cover up the origin and destination of the suitcase -- a secret contribution, prosecutors said, sent by Venezuela to bolster the presidential campaign Cristina Fern?ez de Kirchner of Argentina, who went on to win election. Mr. Duran could be sentenced to up to 15 years in prison.

The case has become a symbol of the antagonism between the Bush administration and President Hugo Ch?z of Venezuela, who has used his nation's oil wealth to spread his influence throughout the region.

The scandal has also soured America's relations with Argentina and Mrs. Kirchner, whose campaign was challenged by the revelations of secret donations from abroad.

Mr. Ch?z and Mrs. Kirchner accused the United States of political motivations in bringing charges last December, a contention officials in Washington and Miami have denied.

Whether intentional or not, the eight-week trial in Miami revealed an extensive cover-up effort by Venezuelan officials that reached the highest levels of government, and laid bare a business culture in Venezuela that involves regular bribes and kickbacks to high officials in the government and the military.

The trial provided little in the way of proof that American national security was somehow threatened by the presence of the Venezuelans, who had spent much of their time on the phone and in South Florida restaurants trying to persuade the man caught with the suitcase, Guido Alejandro Antonini Wilson, to keep the truth about the money under wraps.

Still, on Monday American officials sought to portray the investigation and the trial as important to safeguarding national security.

''When unregistered foreign agents believe that they can operate on our soil with impunity and disregard for U.S. laws, it undermines the national security of our country,'' said Jonathan I. Solomon, special agent in charge of the Federal Bureau of Investigation's Miami field office.

Mr. Dur?reacted without emotion as the verdict was read. Edward Shohat, his lawyer, said he would appeal.

Mr. Shohat referred to the trial as a ''political circus in which Franklin Dur?is a pawn of the U.S. government.'' But the lawyer declined to comment on allegations he made in the trial's early days: that the prosecution was a politically motivated effort to embarrass Mr. Ch?z's government. ''There's a lot of concern about that, but I'm not going into further details,'' he said.

The scandal first surfaced in August 2007, when an Argentine policewoman here became suspicious about a suitcase being rolled through customs by Mr. Antonini Wilson. The policewoman ordered him to open it. Nearly $800,000, mostly in $50 bills, spilled out. Argentine officials initially detained him but let him go after charging him with a simple customs infraction.

An international scandal ensued when word soon began leaking out that the cash may have been intended for Mrs. Kirchner, then the leading candidate to succeed her husband, N?or Kirchner, as president of Argentina. By that time Mr. Antonini Wilson was long gone, having hopped a plane back to Miami.

A cover-up effort followed, prosecutors said, directed from Venezuela and reaching up to Mr. Ch?z himself, who assigned his intelligence chief to try to keep Mr. Antonini Wilson silent, according to testimony from witnesses.

Unbeknown to the governments of Venezuela and Argentina, Mr. Antonini Wilson had sought the help of the F.B.I. just days after returning to Florida. He agreed to wear a wire and recorded hundreds of hours of conversations with the Venezuelans.

Three Venezuelans and a Uruguayan were arrested, including Mr. Dur? a longtime friend and business acquaintance of Mr. Antonini Wilson. At secretly recorded meetings in Florida, Mr. Dur?offered to deliver up to $2 million in hush money to make sure Mr. Antonini Wilson's legal troubles in Argentina would go away. Another suspect remains at large.

Three of the four men who were arrested pleaded guilty to the same charges Mr. Dur?was convicted of, and two of them were among the government's star witnesses.

Carlos Kauffmann, a longtime friend and business partner of Mr. Dur? testified that he and Mr. Dur?had been driven to help the Venezuelan government by the promise of more government deals. He said he and Mr. Dur?regularly paid kickbacks to government agencies and state officials in deals that netted the two men tens of millions of dollars.

''Big-time favors, sir,'' he testified, when asked what he expected to get from the Venezuelan government for the effort to keep Mr. Antonini Wilson from talking. Mr. Kauffmann also testified that the Argentine and Venezuelan governments were working together to ensure that an Argentine investigation into the suitcase's origin did not succeed.

When Mr. Antonini Wilson testified, he said that the suitcase was not his and that it in fact belonged to an Argentine official who was also on the plane.

The money, witnesses testified, was sent by Petr?s de Venezuela, the national oil company, which had chartered the private aircraft in Caracas. Mr. Antonini Wilson also testified he had been told $4.2 million more was on the flight to Argentina, and he said there had been previous operations to smuggle in political cash from Venezuela to other countries in the region.


PHOTO: Guido Alejandro Antonini Wilson was caught taking cash into Argentina. He decided to work with the F.B.I.(PHOTOGRAPH BY CARLOS BARRIA/REUTERS)