All states and big cities are required to prepare the plans in the face of potential terrorist attacks using the deadly virus.

"The probability of an intentional release of smallpox virus is low, but because the outcome is so serious, as with any infectious disease we must be ready to respond," said Dr. Paul Effler, chief of the Communicable Disease Division in the state Department of Health.

Effler said vaccinating the response teams enables them to move quickly to protect the public by identifying those needing vaccination to control an outbreak and establishing vaccination clinics.

Smallpox was declared eradicated from the world in 1980, but experts fear that it could be used by hostile nations or terrorist groups in an attack. Intelligence experts believe that at least four nations, including Iraq, have unauthorized stocks of the virus.

President Bush plans to make the smallpox vaccine available to all Americans on a voluntary basis to guard against a bioterrorist attack, senior administration officials said today.

As a first step, the president will order military personnel to begin getting smallpox vaccinations and launch a plan to offer the vaccine to emergency medical workers and response teams within weeks, the officials said.

The general public will be offered the vaccine on a voluntary basis as soon as large stockpiles are licensed, probably early in 2004. Bush will announce his plan Friday.

The CDC asked each state to submit its plan to vaccinate public health teams by Dec. 9 and will review and approve each plan before the vaccinations begin. This is expected to be as early as January, state health officials said.

The Department of Health is working with the state's hospitals and the medical community to identify and educate potential health care response team members, it said.

Variations in plans submitted by the states stem partly from the fact that each state is making its own guess about the chances of smallpox reappearing more than 20 years after it was declared eradicated, said Dr. Rex Archer, director of the Kansas City, Mo., health department.

The first group to be offered the vaccine will include those most likely to encounter a highly contagious smallpox patient: people on special smallpox response teams ­ who would investigate suspicious cases ­ and workers in hospital emergency rooms.

Overall, experts estimate that the vaccine will kill one or two out of every 1 million people being vaccinated for the first time, and 15 will suffer life-threatening side effects.