A nation that has clandestine stocks of smallpox might thereby be able to make a strain that would do an end run around the American stockpile of the vaccine, with severe consequences.

But there are persistent rumors of clandestine stocks that terrorists might be able to tap.

But many terrorism experts believe that other nations, including Iraq and North Korea, have clandestine stocks.

A federal intelligence report completed in 1998 concluded that clandestine stocks of smallpox virus probably existed in Russia, as well as in Iraq and North Korea.

But some intelligence experts have long speculated that a few nations, including Iraq, maintain clandestine stocks of the virus.

The smallpox virus exists in laboratories that are overseen by the World Health Organization, although bioterrorism experts believe that clandestine stocks may exist.

In 1998, the Central Intelligence Agency told the White House that Iraq probably kept clandestine stocks of the smallpox virus for military use.

The stumbling block has been intelligence reports that North Korea and Iraq may have retained clandestine stocks for military use.

Whether Saddam Hussein has a clandestine stock of smallpox, along with his known supplies of other germ weapons, is uncertain.

But smallpox has re-emerged as a potential biological weapon, and officials say several nations, including Russia, Iraq and North Korea, may have clandestine stocks of the virus.