The government has not stockpiled enough of the only drug known to be effective against bird flu (search) but is in "aggressive discussions" with its maker to buy more, federal health officials said Thursday.

Enough Tamiflu to treat 2.3 million people is in a national stockpile of drugs and vaccines being set aside in preparation for the next flu pandemic — a worldwide outbreak that influenza specialists fear could be triggered by the increasingly worrisome bird flu in Asia.

Negotiations are under way to buy enough Tamiflu (search) pills for an additional 2 million people, with more purchases possible later.

That still would cover only 2 percent of the population, well short of World Health Organization recommendations that countries set aside enough Tamiflu for one-quarter of their people, said Rep. Tom Davis, R-Va.

"Let me do the math for you: We're about 62 million people under the WHO guidelines," Davis said in chastising the government's top flu officials during a meeting of his House Government Reform Committee.

Other lawmakers wondered why the U.S. is not stockpiling as much as other countries. Manufacturer Hoffmann-La Roche Inc. told the committee that Britain, France, Finland, Norway and New Zealand are placing orders that would cover between 20 percent and 40 percent of their populations.

With today's stockpile, "certainly we don't have enough," said Dr. Anthony Fauci, the National Institutes of Health's infectious disease chief.

He noted that Tamiflu is difficult and time-consuming to manufacture, which "makes it important for us to get our bid in now."

Officials would not estimate how much the nation needs.

Other countries are depending mostly on Tamiflu to fight a bird flu outbreak, while the U.S. also is stockpiling vaccine and would use Tamiflu more to buy time until even more inoculations could be made, said Dr. Bruce Gellin of the National Vaccine Planning Office.

About 36,000 Americans die from regular flu every winter. Because flu virus mutates easily, specialists say it is only a matter of time before a powerful new strain spurs another worldwide epidemic.

There have been three pandemics in the last century. The worst was in 1918, when the Spanish flu killed more than half a million Americans and more than 20 million people worldwide.

Any flu strain could mutate to cause a pandemic. But Asia's bird flu — particularly the H5N1 strain — is of particular concern because people's immune systems have never had to battle it.

The WHO has confirmed the infection in 108 people since January 2004; the vast majority of them caught it from birds. Scientists are watching to see if the strain begins mutating in a way that lets it spread easily among people.

The government's preparation efforts include:

—Buying 2 million doses of an experimental H5N1 vaccine. The first studies of the shot in people began in April. Data on its safety is due later this summer.

—Finalizing a pandemic plan, due in August, that will outline who should be first to get medications and vaccine when a flu virus with pandemic potential begins circulating.

—Funding efforts to increase production of all flu vaccines, not just vaccine against bird flu. This need was highlighted last fall when manufacturing problems cost the nation half its annual supply.

—Exploring whether the drug Relenza would be worth stockpiling against bird flu. It is the same class of medication as Tamiflu but must be inhaled, a big drawback.

Complicating the Tamiflu question is a brewing fight between Roche and the pill's inventor, Gilead Sciences Inc.

Gilead developed Tamiflu, which can be used to treat and prevent regular flu, and licensed worldwide selling rights to Roche in 1996. But last week, Gilead notified Roche that it planned to terminate that agreement, charging that Roche hasn't done enough to promote Tamiflu.

Roche has said it is "deeply disappointed" by Gilead's attempt to take back the drug. The company has doubled production in recent years and has additional expansions under way, chief executive George Abercrombie told the committee as he pledged to work closely with the government on a pandemic stockpile.

Asked by a lawmaker about Roche's cooperation, Fauci would say only, "We, the NIH, are in aggressive discussions."