Jose Padilla, a U.S. citizen arrested in 2002 as he returned to the United States from Pakistan and accused of plotting to blow up radioactive "dirty bombs," had been trained at an al Qaeda weapons camp in Afghanistan and had met repeatedly with top leaders of the terrorist network, who helped finance and equip his plans, a Justice Department official announced today.

Among the key leaders of al Qaeda that mentored or directed Padilla were Mohammad Atef, the organization's operations chief, Khalid Sheik Mohammed, who planned many of the group's operations and Abu Zubaida, one of al Qaeda's top operatives, Deputy Attorney General James Comey said. When Padilla came back to the United States for his mission, they had given him $10,000, a cell phone and names and numbers of people to contact.

Padilla was recruited by al Qaeda and originally trained to blow up apartment buildings using natural gas supplies, Comey said in a press conference. His partner in that scheme was to be Adnan G. El Shukrijumah, a Saudi native who lived in South Florida in the mid-1990s and is still on an FBI most wanted list, but the plan failed because the two men could not get along, Comey said.

Still when Padilla returned to the United States, his handlers in al Qaeda were not sure if he would try to blow up buildings with natural gas or set off a radioactive "dirty bomb." He had offered to do both, Comey said.

Until today, the government had released very little detail about Padilla, who has been classified as an enemy combatant after his arrest at Chicago O'Hare International Airport. His incarceration is at the center of a case that was argued before the Supreme Court in April testing whether the government has the right to detain U.S. citizens under that title and hold them without charge and without giving them access to an attorney. A decision on that case is expected this month.

Comey said his announcement followed an intensive government effort to declassify information gained from the interrogation of Padilla and others. Sen. Orrin G. Hatch (R-Utah), chairman of the Senate Judiciary Committee, has asked the Justice Department to provide information about U.S. citizens being held as enemy combatants and the press conference today was a release of information being given to the committee. The response to Hatch, Comey said, "enables us for the first time to tell the full story of Jose Padilla. It will allow the American people to understand the threat he posed, and also understand that the president's decision was and continues to be essential to the protection of the American people."

Donna Newman, an attorney for Padilla, said Comey's news conference sounded "like an opening statement" and challenged the Justice Department to put Padilla on trial.

"If Mr. Padilla is as dangerous as they say why not simply have the trial?" Newman said in a telephone interview on CNN. " . . . If he was tried and convicted, he would not be a danger."

Comey said the information he was presenting came in part from the questioning of Padilla while he was in military custody and could not be used in a criminal prosecution, although he did not rule out possible criminal charges against Padilla based on other evidence.

"We do not have any plans to present this, the information I have given you today, to a grand jury," Comey said. "I don't believe we could use this information in a criminal case, because we deprived him of access to his counsel and questioned him in the absence of counsel."

Padilla, who left Miami for Egypt in 1998, met a Yemeni recruiter for al Qaeda while Padilla was making the hajj Muslim religious pilgrimage to Saudi Arabia in March 2000, according to Comey. He eventually traveled to Afghanistan that year, where he applied in a typewritten form to join an al Qaeda training camp. That application was discovered by the FBI after the war in Afghanistan.

Padilla has told investigators that he attended the camp in September and October of that year, "with the understanding" that he would be sent to Chechnya to help Muslim fighters there who oppose Russian rule, Comey said. The training included handling weapons and explosives such as dynamite, mines and C-4 plastic explosives.

It was while in Afghanistan he met al Qaeda's military commander, Muhammad Atef, who asked him to undertake a mission to blow up apartment buildings in the United States, Comey said. Padilla then received further training and was paired up with Shukrijumah, whom he had known before in Florida. "They learned how to seal an apartment to trap the natural gas and to prepare an explosion using that gas that would have maximum yield and destroy an apartment building," Comey added. But the partners could not get along and the plan was temporarily put aside.

Padilla returned to live with Atef, but his mentor was killed during a U.S. bombing raid in the Afghanistan war. Padilla decided to flee Afghanistan for Pakistan, where he approached Zubaida and suggested that he could deploy a "nuclear bomb" in the United States, Comey alleged.

Although Zubaida was skeptical of the plan, he sent Padilla and an accomplice to meet with Mohammed about it. Mohammed was also skeptical and urged the men to return to the original plan of blowing up apartment buildings. In fact, he suggested that they hit 20 buildings, but Padilla told Muhammed that he could not rent that many buildings without raising attention to himself, Comer said. So Muhammad sent Padilla and his accomplice, who was not named today, on their way with cash.