The latest turmoil in Pakistan has sparked new worry over the prospect that Al Qaeda or other Islamic radicals will acquire access to the country's nuclear arsenal. Pakistan has an estimated 50 nuclear bombs (compared with about 80 in India), which are dispersed throughout the country. U.S. officials acknowledge they do not have as much information about their location and security arrangements as they would like.

Yet despite Pakistan's political convulsions, U.S. officials say their fears about loose nukes are not as great as they once might have been. After the 9/11 attacks, then-Secretary of State Colin Powell and his deputy Richard Armitage discussed the problem with Pakistani President Pervez Musharraf. According to two former U.S. officials familiar with the matter, Musharraf agreed to install safeguard mechanisms that would "lock" nuclear weapons if they should fall into unauthorized hands.

Even so, the threat of Pakistan as a "ticking nuclear time bomb" should be a "real concern," said Graham Allison, a former assistant secretary of defense for planning in the Clinton administration who now teaches at Harvard. "It is quite possible to describe scenarios in the destabilization of Pakistan in which control of nuclear weapons would be splintered—and in which some of those splinters could be Taliban or Al Qaeda sympathizers." Those scenarios have taken on new urgency in the past few days, after Musharraf suddenly declared emergency rule, sparking widespread protest throughout the country.

The prospect of Al Qaeda getting ahold of Pakistan's nukes haunted U.S. officials after the September 11 attacks—in part because of intelligence that some of Pakistan's top nuclear scientists were members of Umma Tameer-e-Nau, a shadowy Islamic charity associated with Osama bin Laden. In his memoir published earlier this year, former CIA director George Tenet described how the agency received reports from a friendly intelligence service that, just before 9/11, two UTN leaders met around a campfire in Afghanistan with bin Laden and his principal deputy, Ayman al-Zawahiri, and "discussed how Al Qaeda should go about building a nuclear device."

Those reports, combined with an escalation in Pakistani-Indian tensions, produced widespread alarm among U.S. officials and prompted Powell and Armitage to fly to Pakistan beginning in 2002. Lawrence Wilkerson, Powell's chief of staff at the time, told NEWSWEEK that Powell and Armitage intensely lobbied Musharraf to install the same kind of protective fail-safe systems that the United States uses to guard against accidental or unauthorized launches of nuclear systems.

The systems, known as "permissive action links" (or PALs), require that two separate operators enter codes or turn keys to arm and launch nuclear weapons. Wilkerson said that both India and Pakistan were "very receptive" when U.S. officials explained to them how PALs would help them stand down their nuclear arsenals from what had previously been a "hair trigger" launch status.