NEW YORK -- A former Chicago gang member accused of plotting with al-Qaida to detonate a "dirty" bomb of radioactive material can meet with defense lawyers despite government concerns, a judge ruled Tuesday.

U.S. District Judge Michael Mukasey rejected the government's plea to reverse his decision last year allowing lawyers to consult with Jose Padilla, 31, who was designated an enemy combatant by the White House last summer.

Before Padilla can see a lawyer for the first time since June, ground rules have to be worked out between the sides and possibly the judge. A hearing was set for the end of the month.

Enemy combatants are held without charge or trial and are not allowed to see lawyers. The Bush administration has argued the detentions are constitutional and are necessary to protect national security, a position being challenged in courts and questioned on Capitol Hill.

The government will not release the names of those held as combatants. Just two examples of American detainees are known: Padilla and Yasser Esam Hamdi, a native of Louisiana who was captured in Afghanistan.

Padilla was arrested May 8 in Chicago as he returned from a trip to Pakistan and was held as a material witness in a grand jury probe of the Sept. 11 attacks.

The government said he approached Abu Zubaydah, al-Qaida's top terrorism coordinator, in Afghanistan in 2001 and proposed stealing radioactive material to detonate a bomb in the United States. The government also said he twice met with senior al-Qaida operatives in Pakistan and discussed the dirty-bomb plot.

The government warned that letting Padilla meet with lawyers would interrupt his isolation and result in "grave damage" to its attempt to detect future terrorist attacks. In court papers, the government said that 100 or more attacks had been thwarted after enemy combatants were questioned.

The judge said it "appears likely" that Padilla's detention was not arbitrary and that President Bush was exercising a power protected by the Constitution when he designated Padilla an enemy combatant.

But he added that he cannot be certain unless Padilla has an opportunity to present evidence through a lawyer.

The judge also said he was skeptical that letting Padilla speak with lawyers would ruin the government's chance to learn what it needs to know from him. Padilla is being held in a Navy brig in Charleston, S.C.

Donna Newman, a defense lawyer fighting to meet with Padilla, said she was pleased with the ruling.

"It is comforting for all United States citizens that if they were to be seized by the military and held incommunicado, at least an attorney can have access to them and be their voice," Newman said.

Justice Department spokeswoman Barbara Comstock said the agency would review the decision "in light of our duty to take all steps possible within the law to protect the American people."

William F. Schulz, executive director of Amnesty International USA, called the ruling a small victory.

"The U.S. Constitution grants all citizens basic rights, including the right to an attorney, to know the charges against them and to a speedy and public trial," he said.