Some U.S. hospitals are already struggling to deal with the current flu outbreak. But that is nothing compared to what would happen if a powerful new flu strain exploded into a worldwide flu outbreak, known as a pandemic.

Patients would overwhelm hospitals, and the overflow would have to be housed elsewhere, such as schools — which would already be closed. Nurses, already in short supply, could not possibly get to everyone. And there would be even fewer doctors and nurses once they, too, started getting sick.

There would not be enough antiviral drugs or ventilators to take care of the elderly, who are most at risk of dying from flu.

"Pandemic flu is a special challenge ... it has a much greater potential for the disruption of the function of society," said Dr. Jeffrey Duchin. As chief of communicable disease control, epidemiology and immunization for Seattle-King County's public health department in Washington state, Duchin is one of the many health officials wrestling with the challenge.

"It's arguably the most significant biological disaster that could ever afflict a community," he said.

Many public health officials say the country needs to do much more to ready itself for such a disaster, and U.S. Health and Human Services Secretary Tommy Thompson (searchsaid last week that work is under way on a national preparedness plan.

HHS expects $50 million from Congress for pandemic flu planning, including research into ways of speeding up flu vaccine manufacturing. The department will ask for $100 million more in fiscal year 2005.

A pandemic can happen if different flu strains swap genetic information and mutate into a new strain that people's bodies have no immunity against and that is easily spread from person to person.

Health experts say the world is overdue for such an event.

The last pandemics were the Hong Kong flu in the late 1960s, when 34,000 died in the United States, and the Asian flu of 1957-58 that killed about 70,000 in this country. The 1918 Spanish flu killed roughly 20 million worldwide, half a million of them in the United States.

These days, even an ordinary flu epidemic can kill an estimated 36,000 Americans.

"The world will be in deep trouble if the impending influenza pandemic strikes this week, this month or even this year," wrote Drs. Robert Webster and Richard Webby, of the St. Jude Children's Research Hospital (search) infectious disease department, in an article last month in the journal Science. "The time for talking is truly over. We must be prepared."

In some ways, the country is better prepared than it was a few years ago. The Sept. 11, 2001, terrorist attacks jump-started health agency and government planning for everything from chemical spills to bioterrorism.

But much remains to be done.

Many hospitals have disaster plans that address pandemic flu, but they lack specifics, said James Bentley, senior vice president for strategic policy planning for the American Hospital Association (search).

A pandemic likely would force hospitals to put overflow patients in their hallways or cafeterias, or even into other public facilities such as armories or school, Bentley said.

And only a quarter of state health departments have specific pandemic flu plans, according to a recent study from the nonprofit group Trust for America's Health.

"The only way that large metro areas or any area like ours can be prepared for pandemic flu is through an all-hazards approach that's robust enough to deal with pandemic flu," said Dr. Alonzo Plough, public health director for Seattle-King County. "It's a common kind of defense that would work for a wide variety of agents."

Defense also involves regular updates: 350 hospital, fire and police officials met earlier this month to assess how the Seattle area reacted to the last health crisis, SARS.

"If pandemic flu hit we do not have the level of preparedness that we would like to have," Plough said. "But we're better than we were."

So far this year, 42 children have died of the flu in the United States, a number that worries federal officials. The Centers for Disease Control and Prevention on Friday characterized the outbreak as a likely epidemic and ordered field teams to help states deal with the outbreak.

While the current flu season is not a pandemic, it has shown the difficulty in fighting the disease. There have been flu shot shortages, and the slow process of making the vaccine means no more can be made in time to be effective this season.

"The health care system is clearly stressed and would be stressed further in the event of a pandemic," said Dr. William Schaffner, a Vanderbilt University flu expert. "There's not a solution for a large volume of patients. It's an ever larger problem if it's a pandemic."

Internationally, health experts aren't confident that some countries — as in the case of the early days of SARS in China — will fully disclose everything they know to meet the threat.

The World Health Organization has developed ways to rapidly convey information and provide samples of threatening flu strains to countries, but WHO officials stress that their plan does not enable them to predict when a pandemic might strike. They also warn that many countries lack the ability to adequately prepare for a pandemic.

"I don't think one should ever envision that they're completely prepared," said Bentley of the American Hospital Association. "The difficulty with pandemic flu ... is that it's a communicable disease and if you can't contain it at the start — and you often can't — it can get away from you."