Filed at 8:45 p.m. ET

WASHINGTON (AP) -- The Bush administration said Friday it will keep the government's stock of smallpox virus in case it should be needed to develop new vaccines or treatments, putting off yet again a commitment eventually to destroy it.

The virus is supposed to be held in only two locations worldwide: the Centers for Disease Control and Prevention in Atlanta and a similar facility in Russia. Many bioterrorism experts believe that other nations, such as North Korea or Iraq, may have samples that could be unleashed.

Health and Human Services Secretary Tommy Thompson said he agrees with scientists who argue that the United States should hold onto its stock in case it is needed to develop new treatments or a vaccine that is safer that the one that exists today.

``Until we have developed our defenses, we must keep this killer secure but available for needed research,'' he said in a statement. ``Events of the last two months make all too clear that if smallpox virus fell into the wrong hands, it might be deliberately unleashed. While the chance of release of smallpox remains small, it is nonetheless real, and we must be prepared to combat it.''

After the disease was declared eradicated in 1980, the World Health Organization brokered an agreement that nations would send their stocks to the United States and Russia. They were eventually to destroy the stocks after scientists had completed study on the virus and had made sure the disease actually was gone from the world.

But in 1999, the Clinton administration decided not to destroy the U.S. stock but promised to return to the issue in 2002.

One of the most prominent critics of the 1999 decision is now Thompson's top bioterrorism adviser: Dr. D.A. Henderson, who lead the smallpox eradication campaign. In a speech just last week, Henderson argued that the Clinton administration was wrong to keep the smallpox on hand. Destroying it, he said, would decrease the likelihood that it would be released.

HHS spokesman Kevin Keane said he doesn't know if Henderson was consulted about the decision to keep it.

Thompson said in his statement that he had informed the World Health Organization of the administration's decision. Officials from WHO could not be reached for comment Friday either in Geneva, Switzerland, or Washington.

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On the Net: Department of Health and Human Services bioterrorism page: http://www.hhs.gov/hottopics/healing/biological.html

Centers for Disease Control and Prevention smallpox page: http://www.bt.cdc.gov/Agent/Smallpox/Smallpox.asp

World Health Organization biological and chemical weapons page: http://www.who.int/emc/deliberate--epi.html

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