WASHINGTON — Federal health officials are stockpiling enough smallpox vaccine for every man, woman and child in America in case the deadly, highly contagious virus is ever used as a weapon. But there is growing debate about who should be vaccinated and when.

Despite calling smallpox “among the most dangerous of all potential biological weapons,” the Centers for Disease Control and Prevention’s current plan does not offer Americans the option of getting vaccinated before any attack occurs.

The primary reason: The CDC anticipates one or two deaths for every 1 million doses of vaccine given — or about 280 to 560 deaths nationwide.

“If everybody received a vaccine, there are some for whom that vaccine might be fatal,” President Bush said in July. “And I worry about that.”

Critics of the cautious approach say it could cost tens of thousands of lives if a large urban area were hit. Once a person has the disease, there is no treatment that can stop it from running its course.

“There will be some deaths from the vaccine, and we need to prepare for that,” said Dr. William J. Bicknell, a professor at Boston University’s Department of International Health. “But you have to compare that to a probable 30 percent death rate of everybody infected in an attack. A smallpox attack would make anthrax look trivial.”

In a democracy, citizens must have the power to weigh the risks and make their own decisions, said Sen. Bill Frist, R-Tenn., a medical doctor and influential GOP leader.

“I believe the threat of a smallpox attack outweighs the risks of providing smallpox vaccinations to a well-informed public,” Frist wrote in an Aug. 9 opinion piece in The New York Times.

The last naturally acquired case of smallpox was in 1977 in Somalia. Although smallpox was officially eradicated from the globe in 1980, the United States and Russia still have stocks of the virus. The World Health Organization recommended that these stocks be kept to vaccinate laboratory workers who handle vaccinia virus — a live virus similar to smallpox — and to safeguard the public from a deliberate or accidental release of smallpox virus.

Intelligence experts fear terrorists or rogue nations such as Iraq could get, or may already have acquired, some of those stocks.

Routine vaccination against smallpox ended in the United States in 1972. Half the U.S. population has never been vaccinated against the disease, and it’s unclear what immunity — if any — the other half may have since their vaccinations were designed to last about 10 years.

Tommy Thompson, secretary of health and human services, is expected to decide on a vaccination policy later this year. The Advisory Committee on Immunization Practices — an independent panel of experts — has recommended that front-line health care and emergency workers be vaccinated. The CDC said a small group of its workers who would respond to a bioterrorism attack already have been vaccinated.

Thompson’s department estimates it will have 200 million new doses of smallpox vaccine stockpiled by the end of this year in addition to 85 million doses produced in 1958, said Jerome M. Hauer, acting assistant secretary for public health emergency preparedness.

The vaccines do not contain the smallpox virus. They contain a similar live virus that provides immunity against smallpox.

Bicknell argues that the CDC’s estimates of deaths from vaccines do not take into account that doctors could avoid vaccinating people susceptible to complications, such as those with AIDS and other immune deficiencies.

While much of the public debate has centered on vaccination in the absence of an attack, some scientists are more worried by what they see as the government’s inadequate response plan for an actual event.

The CDC’s interim response plan, backed by the Advisory Committee on Immunization Practices, calls for only limited vaccination in the event of an attack.

Once the first cases of smallpox turned up at emergency rooms and doctors’ offices, health officials would try to track down and vaccinate anyone who came into contact with the sick people. If people are vaccinated within four days of exposure, they may develop a less severe case or escape the disease entirely.

But thousands of people could be infected while the government is trying to find those who were exposed to the virus, researchers said in a paper published in July in the Proceedings of the National Academy of Sciences. The National Academy of Sciences is an independent group of experts that advises the federal government.

“Trying to track down who sneezed on whom doesn’t make sense,” said Edward H. Kaplan, a professor at Yale University’s Schools of Management and Medicine who co-wrote the research paper and recently presented his findings to CDC officials. “If I’m sick and I’ve been running around, I’m not going to remember everybody I came into contact with.”

Kaplan and his research colleagues advocate mass vaccination of everyone in the city or area that was attacked from the moment the attack is recognized. The difference in lives saved, the researchers say, would be enormous.

If terrorists unleashed a smallpox attack against an urban area of 10 million people — and 1,000 people initially came down with the disease — a targeted vaccination program could result in 110,000 deaths compared with 560 under an immediate mass vaccination scenario.

Despite the CDC’s written plan, federal health officials would be “very flexible” in responding to a real attack, Hauer said.

“We are not married to any one solution,” he said.

But that’s not much comfort to Kaplan.

“If we don’t have a clear plan,’’ he said, “it could cost us in lives.’’

(Contributing: Ellyn Ferguson, GNS)