The White House has announced new plans to prepare the U.S. for the possibility that avian influenza will become easily transmissible among humans and spur a pandemic that could kill as many as two million Americans.

The U.S. preparedness implementation report outlines more than 300 "critical actions" that would have to be taken in the case of a bird flu pandemic. Many of the precautionary steps are already in place, according to the plan released Wednesday.

The Bush administration has requested $7.1 billion to prepare for such a pandemic.

In the worst-case scenario, the report said, 30 per cent of all Americans could come down with the disease - for a total of 50 million cases.

As well, 40 per cent of the U.S. workforce could be off the job for weeks at a time because of illness or quarantines.

The H5N1 form of bird flu has killed 113 people around the world, most of them children or young adults, since the current outbreak began in 2003. So far, almost all of the cases have occurred where humans live in close proximity to infected birds such as domestic poultry.

Flight restrictions not ruled out

Shutting the border to Canada is an "impractical" way to stop the spread of the disease because people can be contagious for 24 to 48 hours before they start to show symptoms, the report said.

However, Fran Townsend told reporters in Washington, D.C., that the government is not ruling out banning or quarantining flights from flu hotspots to slow spread of the disease.

"We recognize that we cannot make these decisions in a vacuum and must consult with our international partners," said Townsend, who is President George W. Bush's homeland security adviser.

"We cannot forget that a pandemic occurs because of the spread of the disease from one person to another," Townsend added, stressing that individuals can play a role in keeping the country healthy by observing good rules of hygiene.

Businesses asked to change practices

Among the recommendations in the report are some aimed at businesses throughout the country.

Managers will be asked to hold more teleconferences if a pandemic starts spreading around the globe, restrict corporate travel and keep workers at least a metre apart from each other to reduce close contact that could speed the flu's spread.

The report also suggests that authorities might divert flights with possibly infected passengers on board, order flight crews to wear face masks and impose quarantines.

The plan says the National Guard would contain any violence if civil unrest breaks out as a result of a pandemic.

Townsend said the blueprint for action is silent on some issues, including the kind of people who might get preferential access to vaccines and anti-viral medications in case of a pandemic.

Development of a specific vaccine would have to wait until a human-to-human form of the disease is confirmed to be spreading and scientists can gather samples.