Washington ? Officials weighing whether to dispense smallpox vaccine to the nation were presented with the possibility Saturday that the virus might be a more effective terrorist weapon than they thought.

U.S. researcher Alan Zelicoff, drawing on long-secret Soviet documents, reported on an isolated 1971 outbreak that he said appeared to have been caused by smallpox that was tested as a weapon and carried miles through the air.

If that was in fact the cause of the outbreak that killed three people, it suggests that a disease known to spread mainly in close quarters also has the potential to be used as a weapon of mass infection from farther away, perhaps from one end of a city to the other.

While Zelicoff’s analysis created something of a sensation at a conference of scientists and health officials, not all were buying the theory and some were openly skeptical.

“I see nothing whatsoever that’s new,” said D.A. Henderson, who advises the government on bioterrorism and led the campaign that eradicated smallpox more than 20 years ago. He called the report alarmist.

Public health officials are stockpiling more than 300 million smallpox doses, enough to protect everyone in the country in the event that terrorists somehow get hold of the virus and use it to attack. Authorities expect to have enough on hand by the end of the year.

Meantime, they are deciding whether to offer the vaccine to the public absent any smallpox cases.