MIAMI — A Venezuelan businessman acted as an unregistered foreign agent last year while trying to cover up an election scandal that exploded into a Latin American imbroglio, an American prosecutor said yesterday in opening remarks at his trial.

Franklin Duran, 40, is accused of acting for President Chavez’s Venezuelan government in trying to convince a Miami businessman to hide the source and destination of $800,000 the man toted in a suitcase seized at an airport in Argentina. The cash was intended to support the campaign of Cristina Fernandez de Kirchner, who was elected Argentina’s president October 28, a prosecutor told jurors yesterday in federal court in Miami.

“Mr. Duran acted as an agent of the government of Venezuela in the United States of America,” an assistant American attorney, Thomas Mulvihill, said. “That is a violation of our law.”

A Duran attorney, Edward Shohat, used his opening statement to “hotly contest” Mr. Mulvihill’s account, saying his client never pressured the businessman, Guido Alejandro Antonini Wilson, when Mr. Antonini returned to Florida after the seizure on August 4, 2007. Mr. Shohat disputed Mr. Mulvihill’s claim that Mr. Duran was an unregistered agent for Venezuela’s intelligence agency, known as DISIP.

“He did not come here as an agent of deceit of the Venezuelan government or any agency of Venezuela to convince Alejandro Antonini to lie about the source of the $800,000,” Mr. Shohat said.

Mr. Shohat said Messrs. Antonini and Duran were friends for 20 years, and worked together on business deals in Venezuela. Mr. Antonini, who was owed “an extremely large commission” by a Duran company, “begged Frank for help” following the cash seizure before betraying him to the Federal Bureau of Investigation, Mr. Shohat said.

Mr. Mulvihill said Mr. Antonini went to the FBI and secretly taped Mr. Duran and others. Those tapes, made between August 23 and December 11 last year, make “very clear” that Mr. Duran and others pressured Mr. Antonini not to tell Argentine officials the cash came from the Chavez government to aid Ms. Fernandez. He said that at the FBI’s behest, Mr. Antonini wrote Mr. Chavez demanding $2 million to take care of his family.

Mr. Duran was arrested December 11 with three other South American men. They later pleaded guilty and said in court that DISIP played a central role in covering up the payment of the $800,000. A fifth man was indicted and remains a fugitive.

Mr. Duran is charged with conspiracy and acting as an unregistered agent of the Venezuelan government. He faces as many as five years in prison on the conspiracy charge and 10 years on the other charge. He also faces possible deportation.