But an Associated Press survey of states suggests wide variations in how many people they plan to vaccinate and how many hospitals they expect will participate in this first round of inoculations.
States were supposed to submit their plans for the first stage of smallpox vaccinations by Monday to the federal government. Immunizations will begin after a presidential announcement, expected in coming days, and states have been told that they'll have 30 days to deliver the shots.
The first group to be offered the risky but effective 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.
Nationwide, federal officials have said that about a half million people were expected in this first group, but officials said Monday they now expect the numbers to be slightly lower. They now estimate that up to a half million will be offered the shots, but that some of them will decline to be vaccinated and others will be screened out because of conditions that make them susceptible to dangerous side effects.
No matter what the final number, the AP survey suggests that these shots are not likely to be evenly distributed across the country.
Georgia is planning shots for just 300 to 500 people, while Louisiana anticipates as many as 20,000. California has requested 70,000 doses of the vaccine, where Michigan is asking for just 5,000 to 7,000.
In Michigan, the state plans to offer the vaccine at only about 30 hospitals. "We don't necessarily need it in every corner or at every hospital," said Geralyn Lasher of the Michigan Department of Community Health.
Twice as many hospitals are expected to participate in Montana, and North Dakota hopes to have at least one team of 15 vaccinated health care workers at each of the state's 46 hospitals.
In North Dakota, the state's vastness and lightly populated rural areas make it important that all hospitals are capable of helping a smallpox victim, said Tim Wiedrich, bioterrorism coordinator for the North Dakota Health Department.
"We really believe that it's likely that smallpox patients could present themselves at any of our hospitals," he said.
Federal officials plan to review the number and types of people included in each state's plan and make sure they are comprehensive, said Jerry Hauer, the top bioterrorism official at the Department of Health and Human Services. He said he's not surprised by the variation.
"We wanted to give them that flexibility," he said.
The variation partly stems from the fact that states are each making their own guesses 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. No one knows if smallpox will ever return, but experts suspect that hostile nations and possibly terrorist groups have the virus and could unleash it in an act of bioterrorism.
Others say that the variation among the states is likely to even out after vaccinations begin, with some states asking for more vaccine and others winding up with more than they need.
Plans being submitted to the Centers for Disease Control and Prevention address a wide range of details about the first phase of smallpox vaccinations.
States were asked to explain who would be offered the shots, timelines and locations for delivering them and a plan for ensuring those at particular risk of severe side effects do not get vaccinated.
Once the vaccinations begin, states will be required to keep detailed track of how many people suffer reactions, with reports due twice a week to the CDC.
They are climbing a logistical and medical mountain not ventured in three decades, when routine smallpox vaccinations ended in the United States as the disease waned.
It represents "one of the most complicated logistic activities any state and local agency will have to undergo," said Michael Osterholm, a bioterrorism expert at the University of Minnesota who is advising federal officials on smallpox planning.
The disease, which historically killed 30 percent of its victims, was once one of the world's most feared. At the same time, experts estimate that the vaccine will kill one or two out of every million people being vaccinated for the first time, and 15 will suffer life-threatening side effects.
The major question being debated within the White House is how fast to proceed in offering the shot to the general public.
There is widespread agreement, though, on the first stage of vaccinations. A second stage is likely to cover other health care workers and first responders, totaling as many as 10 million people nationally.
As they begin vaccinating, federal and state authorities will mount an education campaign to help people decide whether to get the shot.
In the end, each person will be forced to consider the same questions Mr. Bush and other top federal officials have been struggling with for months, said Dr. Jimmy Guidry, state health officer for Louisiana.
"It boils down to an individual perception," he said. "Is this risk real or not?"
By Laura Meckler