DENVER - Everything is falling into place for the federal government to start inoculating health workers to protect them against a possible bioterror attack with smallpox, top health officials said Thursday.

The smallpox vaccine sailed through initial safety tests. Vaccine maker Acambis of Cambridge, Mass., is on track to deliver 209 million doses to the government, some by end of this year, the company's chief scientist said.

The federal government has set up an elaborate safety system for expected dangerous side effects. They could include some deaths and thousands of serious illnesses, according to the Centers for Disease Control and Prevention.

Now all that's needed is a go-ahead from President Bush.

The president must decide how many health and emergency workers will get the vaccine as a bioterror preparedness measure, as well as whether the inoculations will be offered to the general public.

Health officials are ready to vaccinate soon after Bush decides, said Dr. James Hughes, director of the CDC's National Center for Infectious Diseases. In order to get vaccinations done quickly, the CDC will use old stockpiled vaccines - made from scraping the skin of cows deliberately infected - before shifting to the new cloned vaccine being produced by Acambis, he said.

"There are a lot of preparations that have been done," Hughes said Thursday at the American Society of Tropical Medicine and Hygiene's convention in Denver.

A special CDC advisory committee recommends voluntary vaccinations for 500,000 health workers who would have the first contact with smallpox victims. After that, up to 10 million other health workers, police, firefighters and paramedics should get the vaccine, and then it should be offered to the general public on a voluntary basis, top health officials recommended to the president this fall.

Smallpox is one of the deadliest and most contagious diseases in human history, killing about 3 out of 10 people who contract it. It was eradicated worldwide 25 years ago. Small samples of the virus are stored in two labs, one in the United States and one in Russia. However, there have been reports that some countries or terrorists may have smallpox cultures that could be made into a weapon.

Officials fear Iraq has such cultures, but there is no evidence of that.

There is no controversy over the federal plan to quickly vaccinate people after a smallpox attack. The debate is over vaccinating people before an outbreak, because it involves using a live vaccine that contains a weak but related pox virus called vaccinia.

Acambis chief scientific officer Thomas Monath said a test of 30 people using the vaccine found little difference between it and the old one commonly used before the disease was eradicated. There were no major side effects, although everyone vaccinated had skin reactions, two-thirds felt headaches, and one-quarter developed muscle pains. Early tests in mice and monkeys show that the new vaccine may produce fewer side effects in the nervous system, a nagging problem with the old one.

The CDC calculates that out of every million people vaccinated, the vaccine would kill two people, give 52 people life-threatening illnesses and infect 1,000 people with serious but not life-threatening reactions.

That's no worse than what happened with the old vaccine, which was given throughout the United States in the 1950s and `60s to schoolchildren until smallpox's eradication made vaccinations unnecessary. A new study said that 36.4 percent of the people vaccinated in the past missed school, work or other events because of side effects from their inoculations, said epidemiologist Scott Campbell with the

CDC's newly formed Smallpox Immunization Safety System. Normal mild bad reactions include sore arms, fever and body aches.