A top federal health official and several prominent medical experts suggested Thursday that voluntary vaccinations for smallpox may be appropriate, three decades after immunizations stopped in this country.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and other researchers said they want to open a national debate on mass inoculation to prepare the nation for an unlikely--but potentially devastating--bioterrorist attack.

The smallpox virus, which is highly contagious, was eradicated worldwide in the 1970s, but officials are worried that vials of the virus kept in storage in the former Soviet Union may have fallen into the hands of Iraq or North Korea. No concrete evidence of this has been made public.

Restarting vaccinations, raised as a possibility in several medical journal articles and at a news conference Thursday, runs counter to current smallpox recommendations from the Centers for Disease Control and Prevention. In one of the articles, Fauci calls the desire for access to vaccinations "reasonable."

Late last year, with only 15.4 million vaccine doses on hand, the CDC concluded that the best way to contain a smallpox outbreak would be to identify cases, quarantine those infected and try to vaccinate anyone possibly exposed.

Now, however, supply is becoming less of an issue. The government is expected to announce today that it is acquiring an additional 70 million to 90 million doses held by a manufacturer. In any case, the government is on track to have enough vaccine to treat all Americans by the end of the year, making it possible to reexamine the CDC's proposal.

"Despite the fact that mass voluntary vaccination is not recommended in the CDC plan," Fauci wrote in a New England Journal of Medicine editorial released Thursday, "there are many who would like to have the opportunity to make their own decision about smallpox vaccination."

Without directly endorsing vaccination, Fauci said that "the strongest argument for preemptive mass vaccination is that it would eliminate smallpox as an agent of bioterrorism. Accordingly, it would eliminate the disarray, confusion and panic that would most likely accompany simultaneous attacks at multiple locations."

He said the downside is that the approach carries serious risks that people need to be aware of. Of every million people vaccinated, one to two will die and hundreds more will become seriously ill, studies show.

"In most circumstances, that would be unacceptable," said Dr. Edward W. Campion, a senior deputy editor of the New England Journal. But "'we now fear bioterrorism in a way [that] seven months ago was unthinkable," he added, cautioning that any decision would have to be made on rational, not emotional, grounds.

It is unclear how voluntary vaccinations would work, although experts said Thursday that public health officials, hospital workers, firefighters and police officers would probably be first in line.

Health and Human Services Secretary Tommy Thompson, who will be heavily involved in making the administration's decision on this issue, said at Thursday's news conference that he still backs the CDC's rapid-containment policy, given the current vaccine supply. But he did not reject the idea of a change, saying more discussion is necessary about voluntary vaccination.

"There is certainly discussion going on . . . and that discussion will continue as further doses of the vaccine [are] made available," he said.

Fauci, a close advisor to Thompson, went one step further. "Any time you do have an open discussion, you almost by definition open the door for reconsideration as things evolve."

Though Fauci declined Thursday to say whether he supports voluntary vaccination as public policy, he said at a Senate hearing in November that he would take the risk of having his own family vaccinated, given the choice.

Fauci said researchers are working to develop a smallpox vaccine with fewer side effects. If that happened, he said, the decision to use widespread inoculation would be easy because the threat of attack could be eliminated with few risks.

Concern about a smallpox attack has run high in Washington since anthrax-laden letters sent through the mail system shut down parts of Capitol Hill last fall and turned up elsewhere too. Five people were killed, at least 13 others sickened and tens of thousands of people were forced to take antibiotics in an attack that remains unsolved.

At a November hearing to explore U.S. vulnerability to a smallpox attack, Sen. Arlen Specter (R-Pa.) said the decision to take the smallpox vaccine should not be left up to the government.

"Tell the American people what the risks are, have the vaccine available and let them make the decision," he said.

On Thursday, Health and Human Services officials announced research findings that could make voluntary vaccination more feasible.

One study released Thursday by the New England Journal found that a 15-million-dose stockpile of smallpox vaccine could be diluted fivefold without compromising effectiveness, which would produce enough doses to inoculate 75 million Americans. Given those results, the stockpile of an additional 90 million doses expected to be announced today, would make it possible to treat most Americans much sooner than expected.

The call for mass vaccination grows out of the belief that the government is ill-equipped to contain an outbreak once it begins. About 157 million U.S. residents have been vaccinated for smallpox, but it is unclear how long that protection lasts. An additional 119 million Americans were born after the program of mass vaccination was terminated in 1972.

In the New England Journal, several experts said that because of the numbers of people unprotected, the CDC's strategy of "containment" is unlikely to work in a deliberate attack. "Widespread, voluntary vaccination before exposure will greatly reduce the number of victims, if an attack occurs," wrote Dr. William J. Bicknell, a Boston University professor and former director of the Massachusetts Department of Public Health.

The post-outbreak containment approach advocated by the CDC would probably result in thousands of deaths before the public health system even had a chance to respond, said Charles Peña a defense policy expert at the Cato Institute, a Washington-based libertarian think tank. "If it's the government responsibility to protect against a future attack, the best way is to take preventive measures, not responding afterwards."

But some public health experts called voluntary vaccination a ridiculous idea. Leaders of the global eradication campaign said high levels of vaccination don't keep the virus at bay.

In Bangladesh, for instance, 80% of the population was vaccinated in 1972, but the country still reported 70,000 infections. Four years later, after health officials employed a strategy of rapid containment, the nation had no cases even though only 78% of the population was vaccinated.

"I say at the moment, the risk of a complication from smallpox [vaccine] is far higher than the risk of smallpox," said Stanley Foster, a former federal health official who headed the eradication effort in Bangladesh.

Smallpox symptoms, including high fever, fatigue, and severe headaches and backaches, appear about 12 to 14 days after exposure. A rash develops on the face, arms and legs, then quickly spreads to the rest of the body.

The virus is not contagious before symptoms appear. But once pox develop in the mouth, the disease can be spread by coughing, shedding scabs or talking to anyone within a few feet.