As fears of bioterrorism subside and worries about a SARS pandemic grow, public health officials are retreating from the Bush administration's ambitious campaign to vaccinate millions of people for smallpox.

The first stage of the vaccination program, designed to inoculate smallpox-response teams in every hospital in the country, effectively flopped: only 33,000 of the intended 450,000 health-care workers were inoculated.

Tomorrow, an Institute of Medicine advisory panel overseeing the program will get an update from federal, state and local public-health officials.

Those officials are now redefining what it means to be "prepared" for a smallpox attack - while grappling with the more urgent threat of severe acute respiratory syndrome (SARS), the new virus that has struck Asia and Canada.

"Right now we are working with each of the states to get a feel from them about where they think they are in their [smallpox] preparedness," said Michael Sage, deputy director of terrorism preparedness at the Centers for Disease Control and Prevention. "It isn't one answer. It is 50 answers."

In many states, including Pennsylvania and New Jersey, health officials say the new answer focuses less on numbers and more on the ability to detect and contain a smallpox outbreak and mobilize emergency vaccination clinics.

"The success of the program cannot just be measured by numbers," said Eddy Bresnitz, New Jersey state epidemiologist.

In the first phase of New Jersey's program, which ended this month, 657 people were inoculated - 14,400 fewer than the state was prepared to vaccinate. New Jersey plans to evaluate the program before continuing, Bresnitz said. Pennsylvania has vaccinated 93 of a planned 22,500 health-care workers; state health officials say they still hope to inoculate 4,500 people by midsummer.

Even critics praise the administration and the CDC for stockpiling enough vaccine to inoculate every American, developing a system to distribute the vaccine, and training a cadre of professionals to administer it.

But it's a far cry from the program President Bush billed as a key part of his strategy against bioterrorism.

Despite the resistance to the first part of the smallpox program, administration officials say they are going ahead with the second phase, originally aimed at vaccinating millions of police, health and emergency workers.

The second phase, many observers believe, will be just as unpopular as the first.

"I see no reason at all" for more inoculations, said Marilyn Hostetter, a nurse and officer of SEIU Nurse Alliance, the largest health-care union in Pennsylvania. "We're advising our members not to get vaccinated" unless smallpox reappears.

The resistance stems from several concerns. The vaccine has dangerous, occasionally deadly, side effects (heart inflammation was added to the list after it occurred in several dozen new vaccinees). And Congress could not agree until earlier this month on a liability and compensation plan, which some union leaders say is inadequate.

Finally, there was widespread skepticism about the need for pre-attack vaccination. There was no proof that Iraq possessed smallpox, and even if an attack occurred, inoculation days after exposure to the virus can still ward off the disease.

"I don't like to say, 'I told you so,' but the desire of this administration to be seen as doing something to protect against terrorism has led to less than judicious use of resources," said Nicholas King, a bioterrorism expert at the University of California, San Francisco.

The government's own smallpox advisory committee initially recommended pre-attack inoculation of only about 15,000 health-care workers in selected regional hospitals. The panel noted that smallpox is not contagious until the pox appear a week or two after infection, allowing time to identify, quarantine and vaccinate exposed people - a strategy that helped eradicate smallpox worldwide by 1980.

All but one panel member - Paul Offit, a vaccine expert at Children's Hospital of Philadelphia - later endorsed the administration's more ambitious immunization plan.

Now, even though twice as many people have been vaccinated as the advisory panel originally recommended, they are far-flung and uncoordinated.

"Now we have an average of five vaccinated workers per hospital, so to say we've created... a first line of defense is wrong," Offit said.

Some observers see parallels between the smallpox campaign and the swine-flu debacle in 1976.

That year, a new swine flu-type virus infected 500 soldiers at Fort Dix, killing one - then mysteriously disappeared. President Gerald R. Ford and his top health officials rejected the idea of simply developing and stockpiling a new vaccine, and instead ordered vaccination of all Americans.

The flu did not reappear - and the program was halted after the new vaccine turned out to cause a rare but sometimes deadly paralysis.

The driving fear in 1976 was that a deadly flu would ignite an worldwide pandemic like the one that killed tens of millions in 1918.

Today, the fear is terrorism.

"The administration is fighting Sept. 11 and the anthrax attacks, during which they were accused of not doing enough to protect the public," said Robert J. Blendon, a Harvard University professor of health policy and political.

"But now, the Iraq war is over and [biological weapons] have not been found yet. So the question is: How great a risk is smallpox? Is there really a risk? If not, why should I take a risk to be vaccinated?"