Updated

The Pentagon has readied a plan for vaccinating some U.S. troops against smallpox and is awaiting White House approval before giving the first shots, according to a senior defense official.

Amid heightened concerns about biological warfare, the Pentagon is pushing to provide every available form of protection for troops who might be exposed to germ weapons in Iraq or elsewhere. U.S. officials said this week that they believe Iraq is among four nations that have unauthorized samples of smallpox; the others are Russia, North Korea and France.

Defense Secretary Donald H. Rumsfeld has not yet given the go-ahead to implement the smallpox inoculation plan, according to the defense official who discussed it on condition of anonymity. Rumsfeld met with President Bush on Thursday morning and planned separate discussions with other members of the president's national security team.

White House deputy press secretary Scott McClellan said Bush has not made a decision. Another adviser said a decision does not appear imminent.

The Health and Human Services Department has set aside about 1 million doses of smallpox vaccine for the military. Those doses are expected to be provided from the 1.7 million that have been licensed by the Food and Drug Administration.

The federal government has tens of millions more doses on hand, but they have not yet been licensed and would have to be administered as an experimental drug.

Hundreds of thousands of U.S. troops have received vaccines to protect them against anthrax, and after a long pause in that inoculation program, the pace of vaccinations was accelerated in September, officials said. It is believed that Iraq has substantial amounts of anthrax that it could use against invading U.S. troops.

Smallpox vaccinations for troops could begin as early as this month, officials said, depending on the pace of coordination with the White House and other government agencies.

First to receive it would be those the Pentagon calls "first responders" — troops responsible for assisting in domestic disasters, such as a bioweapons attack. They include medical specialists. Next to get it probably would be troops in combat units designated to deploy first in a major military crisis abroad, such as an invasion of Iraq.

As many as 500,000 troops might eventually be inoculated, according to another senior defense official. Of the 1.4 million men and women in the active-duty military, fewer than half have ever received the smallpox vaccine, the official said.

For the civilian population, top federal health officials have recommended making the vaccine available in stages, beginning with people who work in hospital emergency rooms; then other health care workers and emergency responders; and finally the general public.

The White House is still considering how quickly to move — specifically, whether to wait until the vaccine is licensed or to offer it more quickly.

Smallpox was declared eradicated from Earth in 1980, and routine vaccinations in the United States ended in 1972. All stocks of the virus, except those stored at official labs in Atlanta and Moscow, were supposed to have been destroyed.

It is a powerful weapon: It kills 30 percent of its victims, is highly contagious and has no known treatment.

But while the disease is frightening, so is the vaccine. It's made with a live virus called vaccinia that can cause serious damage to people vaccinated and those with whom they come into close contact. Health officials estimate that about 15 out of every million people being vaccinated will face life-threatening side effects, and one or two of those 15 will die.