MIAMI — The trial of suspected Al Qaeda operative Jose Padilla opened yesterday with federal prosecutors arguing that the American citizen and two co-defendants were key players in a terror support cell that provided equipment, money, and Islamist fighters to extremist groups around the world.

“The defendants were members of a secret organization, a terrorism support cell, based right here in South Florida,” Assistant U.S. Attorney Brian Frazier told jurors in his opening statement. “The defendants took concrete steps to support and promote this violence.”

Attorney Jeanne Baker, representing co-defendant Adham Amin Hassoun, called the prosecution’s case “a totally false picture.”

While Mr. Hassoun, a 45-year-old Palestinian Arab, had strong political opinions and was “a big talker,” his sole aim in providing support for groups overseas was to assist oppressed, persecuted, and needy Muslims, Ms. Baker said.

“He was helping to protect and defend Muslims from murder. That is not an intent to commit murder. That is just the opposite,” she said.

Prosecutors and defense attorneys have spent months battling over issues ranging from torture allegations to the meaning of “jihad.” They pored over classified material and Arabic translations and traveled overseas to interview witnesses and spent weeks picking a jury.

If convicted, the three defendants could face life in prison. The trial is expected to last into August.

Mr. Padilla, a 36-year-old former Chicago gang member and convert to Islam, has been in federal custody since his 2002 arrest at O’Hare International Airport. He was initially accused of plotting to detonate a radioactive “dirty bomb” in America and held for 3 1/2 years as an enemy combatant at a Navy brig, but those allegations are not part of the Miami indictment.

He was added to the Miami case in late 2005 amid a legal battle over the president’s wartime powers of detention involving U.S. citizens. His lawyers had fought for years to get him before a federal judge.

In court yesterday, Frazier told the court that Padilla agreed to be recruited by Hassoun as a prospective mujahedeen fighter to be trained by Al Qaeda in Afghanistan.

“Jose Padilla was an Al Qaeda terrorist trainee providing the ultimate form of material support — himself,” Mr. Frazier said. “Padilla was serious, he was focused, he was secretive. Padilla had cut himself off from most things in his life that did not concern his radical view of the Islamic religion.”

Mr. Hassoun and the third defendant, Kifah Wael Jayyousi, 45, provided other Islamist fighter recruits, military equipment, and money for conflicts in Lebanon, Chechnya, Somalia, and other global hot spots, often using Islamic charitable organizations as a conduit, Mr. Frazier said.

The defendants sought separate trials, but their motions were denied by U.S. District Judge Marcia Cooke. She ruled the government had ample evidence that the three were connected in a conspiracy, with Messrs. Hassoun and Jayyousi as jihadist recruiters, fundraisers, and suppliers and Mr. Padilla as one of their recruits.