The initial stage of the decision would see 500,000 military personnel and 510,000 civilian medical workers receive the jab.

A second step would involve up to ten million frontline workers such as police, the emergency services, and other healthcare staff who would be the first to respond to a bioterrorism attack.

The smallpox vaccine would then be made available to any member of the public who wanted one, although it would be accompanied with warnings of the health risks involved and would not be recommended by the authorities.

Mr Bush is expected to publish the details in the next few days after months of agonising. One to three people in the initial wave of one million recipients are likely to die from side-effects of the vaccine, according to estimates by health experts, and dozens of others will contract life-threatening illnesses.

However, Mr Bush has been persuaded that the risks from a bioterrorism attack on US soil are too dangerous to ignore. If there were an outbreak of the highly contagious disease, some 30 per cent of those affected would die and many survivors would be left blind or disfigured, health experts say.

Dick Cheney, the Vice-President, has been the driving force behind preventive vaccinations. Since the immediate aftermath of the September 11 attacks, Mr Cheney has frequently voiced fears that the US was underprepared for a bioterrorism attack.

The wrangle within the White House over the decision to reintroduce vaccinations has been complicated by changing patterns of healthcare which have increased the danger of harmful side-effects for millions of Americans.

Those being treated for cancer or Aids, or who have had courses of drugs which have impaired their immune systems, would be ruled out, even though they would be most at risk of contracting the disease.

France is preparing to administer smallpox vaccinations to an undisclosed number of emergency medical teams, including military and civilian doctors, nurses, drivers, helicopter pilots and administrators.

The Government has also given orders for the preparation of a vaccination programme that would immunise the whole population within two weeks. The Health Ministry said that details of the vaccination plan, drawn up as a precaution against bioterrorism, would remain secret.

The Canadian Government is planning to vaccinate about 500 frontline medical workers, doctors, nurses, and laboratory technicians before the end of the year.

The Government is also negotiating with the pharmaceutical firm Aventis to buy ten million doses of smallpox vaccine, at a cost of about £16 million, which health authorities believe would be enough to immunise the entire country.