The government has about 15.4 million doses of smallpox vaccine stockpiled. A British company, Acambis, is making 54 million doses for delivery next year under a previous contract. The government will need about 250 million more doses to meet its goal, Thompson said.

Dr. Tony Fauci, head of the National Institute of Allergies and Infectious Diseases, said the number of stockpiled doses may be expanded if a dilution experiment is successful.

Researchers are now inoculating volunteers with diluted doses to see if a weaker vaccine will still provide protection. Fauci said the results should be known by February. If the experiment is successful, it could expand the stockpiled doses to at least 75 million, he said.

No American company has made smallpox vaccine since the 1980s, when smallpox was considered eradicated from the world. Most said they would have to start from scratch - installing equipment and developing the expertise - to begin production. The vaccine would have to meet standards set by the Food and Drug Administration.

Doing all that by the end of 2002 could be difficult without some close cooperation with government health agencies, including ``breaking down some barriers'' in regulation, said Nancy Pekarek, a spokeswoman for GlaxoSmithKline.

``Under ordinary circumstances, we're not able to gear up that quickly,'' she said. But Pekarek said GlaxoSmithKline has ``made a commitment to do whatever we can to meet the needs.''

A spokesman for Aventis Pasteur said it was uncertain if his company would even participate. ``We are one of the companies that got a letter, but we have not decided if we will respond,'' said Len Lavenda.

He said Aventis last made smallpox vaccine in the 1970s. ``We don't even have the technique to quickly produce smallpox vaccine by today's standards, (and) we don't know what standards would apply.''

FDA spokesman Larry Bachorik the agency would not cut corners in safety or quality.

``The FDA is committed to work long and hard if that is what is required,'' he said. ``But the FDA will still uphold its same high standards.''

Baxter International spokeswoman Tanya Tyska said Baxter - which has a commercial alliance with Acambis - would commit only to offer ``assistance to accelerate'' vaccine production. ``Baxter's role has not really been determined,'' she said.

Eilene Underkoffer of Merck & Co. would say only that her firm ``was in discussion'' with HHS.

Wyeth-Ayerst Laboratories spokesman Doug Petkus said the letter was still being evaluated. ``We are in discussions with the government about how we can be helpful,'' he said.

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On the Net:

Department of Health and Human Services: http://www.hhs.gov/

Smallpox facts: http://www.bt.cdc.gov/Agent/Smallpox/Smallpox.asp