The Food and Drug Administration has granted a license for the federal government's 30-year-old stockpile of smallpox vaccine, easing the way for millions of Americans to be inoculated eventually against the deadly virus.

Jerome M. Hauer, head of bioterrorism at the Department of Health and Human Services, said the bulk of the first batch of 1.7 million doses had been promised to the Pentagon, which is preparing for potential war with Iraq. The remaining 13.7 million doses could be used to respond to a smallpox attack or to vaccinate emergency responders prior to any attack.

The Bethesda-based FDA approved the license on Oct. 25 but did not announce its decision. In response to inquiries, officials confirmed yesterday that the vaccine had cleared all regulatory hurdles.

Securing the FDA license makes future use of the vaccine, known as Dryvax, significantly easier for federal health officials, said Dartmouth University's John F. Modlin, who chairs the government's advisory panel on vaccines.

"The only legal way to administer an unlicensed vaccine would be under Investigational New Drug regulations," which involve cumbersome informed consent and patient monitoring, he said. "The license will allow the vaccine to be distributed and administered in a more efficient manner."

Last summer, the nation's top bioterrorism experts recommended a three-step smallpox immunization plan. Under the proposal, presented to President Bush by HHS Secretary Tommy G. Thompson, about 500,000 health care workers would be inoculated immediately and serve as the early investigators into any possible outbreak. Later, as many as 10 million police, fire and emergency responders would be offered the vaccine.

Eventually, all 280 million Americans would have the option of being vaccinated, though that would likely not occur until a new batch of vaccine is licensed sometime in 2004.

Several sources have indicated that Vice President Cheney has advocated broad vaccination in part to deter an attack. But Bush has voiced concerns over the vaccine's dangerous, sometimes fatal, side effects and has not yet decided who should be offered it.

In addition to the 15.4 million doses of Dryvax, the government has 75 million doses of vaccine made by Aventis Pasteur Inc. and has ordered 209 million doses from partners Acambis PLC and Baxter International Inc. It could take as long as a year before the latter two vaccines are licensed.

Technically, the Dryvax was licensed when it was made in the 1970s, but manufacturer Wyeth needed supplemental approval for new bifurcated needles and diluent, the liquid material used to reconstitute freeze-dried vaccine, said Karen Midthun, the FDA's director of the Office of Vaccines Research and Review.