A new smallpox vaccine will be provided free to Americans who want it if the vaccine, now being manufactured, passes licensing tests as expected in 2004, Tommy G. Thompson, the secretary of health and human services, said yesterday.

But in a news conference, Thompson repeated President Bush's strong recommendation made Friday that the public not seek vaccination now with an older vaccine because there is no imminent danger of a bioterrorist attack.

On Friday, Bush announced his long-awaited decision to give smallpox vaccinations for the first time in 30 years to select groups of Americans.

In the first stage, about 500,000 frontline military personnel and 500,000 civilian health care workers will get the vaccine. The military began vaccinating Friday afternoon. Vaccination of health care workers will begin late next month.

Immediately after the first stage is completed, up to 10 million health care workers, firefighters, police officers and emergency medical technicians will be offered the vaccine. Despite tremendous logistical challenges, officials hope to finish this second stage in summer.

These people will receive the same vaccine that was used to eradicate smallpox from the world in 1980 and has been stored since then.

When a vaccine made by newer techniques is licensed, probably in 2004, the government will offer it to Americans through clinics but not through private doctors.

Bush said that public health agencies would work to accommodate Americans who insist on being vaccinated now.

How many Americans will choose to get the vaccine now, or in the future, is unknown, federal health officials said in a news conference.

Dr. Julie L. Gerberding, the director of the Centers for Disease Control and Prevention, said that her federal agency had conducted focus groups that found "mismatches" between the public's desire to be protected and its understanding of the risks of the vaccine. Smallpox vaccine is the most dangerous of all human immunizations, and the virus it is made from can be inadvertently transmitted to other people.

More than 140,000 doctors have signed up to participate in educational programs to help them answer questions from patients, Gerberding said. The disease prevention agency is preparing to send about 150,000 educational CD-roms to doctors by the end of the year.

To illustrate the point about misunderstandings, Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, said that when participants in focus groups were asked how many wanted to be vaccinated, about 60 percent said yes. But after health workers explained the dangers of the vaccine, the percentage dropped to 15 to 20 percent, Fauci said.

Federal officials participating in the news conference initially said that Americans would be able to get the new vaccine at their doctors' offices.

But Thompson interrupted and said emphatically that individual doctors would not be permitted to keep the vaccine in their offices.

"It will not be in your doctor's office," Thompson said. "We will not give it up out of our custody. It will not be willy-nilly handed out to doctors across America. We will retain custody of the vaccine."