American terror suspect Jose Padilla learned how to build a radioactive bomb at an Al Qaeda safehouse in Pakistan and may have discussed plots to blow up hotels and gas stations, according to a previously classified government memo.

But the memo, written by Defense Department adviser Michael H. Mobbs and released Tuesday by the Justice Department, states that other intelligence shows Padilla was not a member of Al Qaeda and that there was no timetable for an attack.

Mobbs wrote that some of the people who informed on Padilla may have provided false information to mislead the U.S. government.

The memo was included with a government court filing in which Justice Department attorneys defended the military's detention of Padilla without trial.

Padilla's attorney, Donna Newman, had asked the U.S. District Court for the Southern District of New York to order the government to give Padilla a trial.

In the government's response, officials revealed for the first time how they came to suspect Padilla of being involved in a plot. Two Al Qaeda prisoners held outside the United States fingered Padilla, the memo says.

In 2001, Padilla approached senior Al Qaeda lieutenant Abu Zubaydah with a proposal to conduct terrorist attacks within the United States, the memo states.

Zubaydah, who is now in the custody of the U.S. military, directed Padilla to travel to Pakistan for training in wiring explosives from Al Qaeda operatives. There, Padilla researched how to construct a "dirty bomb" -- a device that spreads radiation without causing a nuclear explosion.

Mobbs writes in the memo that Padilla met with Al Qaeda officials twice. In 2002, he and Al Qaeda officials discussed the possibility of blowing up gas stations or hotels in a series of coordinated attacks on the United States, the memo states.

Some of that information has been corroborated, the memo says, but some "confidential sources have not been completely candid. ... Some information provided by the sources remains uncorroborated and may be part of an effort to mislead or confuse U.S. officials."

The memo states that one of the sources recanted much of the information he provided and one source was being treated with "various types of drugs to treat medical conditions."

Newman, the attorney, did not return calls from The Associated Press late Tuesday.

Some law enforcement officials have suggested that Padilla was not strongly tied to Al Qaeda and was probably sent to the United States with little support. Critics in Congress have accused the Bush administration of overblowing Padilla's arrest to divert attention from questions about terrorism-related intelligence failures.

Padilla, 31, is being held in a military brig in South Carolina as an enemy combatant, a legal designation allowing the government to jail him without formal criminal charges. Newman has argued in court that he is being held illegally and should be released.

Investigators have said they believe Padilla, a Muslim convert and a former Chicago gang member, ventured overseas in search of clerics connected to the most radical branch of Islamic fundamentalism.

In early June, Attorney General John Ashcroft announced from Moscow that Padilla had been arrested in May at O'Hare International Airport in Chicago.