The employees had argued that, as military personnel, they should not be forced to take the vaccine because there is no scientific proof that it is effective for humans, said Mark Zaid, their attorney. The class-action lawsuit had asked the court to block the Pentagon from inoculating the plaintiffs and to rule that the vaccine was improperly licensed by the Food and Drug Administration.

But U.S. District Judge Rosemary M. Collyer ruled yesterday that the FDA "did not act arbitrarily or capriciously" and granted the government's request to dismiss the case.

Zaid said the FDA incorrectly drew conclusions about the effectiveness of the vaccine in people based on old studies involving animals. "This case has repercussions far beyond the anthrax program," he said. "Anyone who is concerned about vaccine safety should be wary of this judicial decision."

The shots have been required for most military personnel and civilian employees assigned to homeland bioterrorism defense or deployed for 15 or more consecutive days in Iraq, Afghanistan or South Korea.

Cynthia O. Smith, a Defense Department spokeswoman, said troops must be vaccinated to protect against biological attacks.

"The FDA has repeatedly found, and independent medical experts have confirmed, that anthrax vaccine is safe and effective," she said. Heidi Rebello, a spokeswoman for the FDA, said the agency is pleased with the decision.

The lawsuit -- filed against the FDA, the Department of Health and Human Services and the Pentagon -- is the third of its kind and the latest chapter in a dispute that has been going on for at least six years.

It follows another suit by the same group that led a federal judge to halt mandatory vaccinations in October 2004 on the grounds that an FDA review of the vaccine was insufficient. The anthrax vaccine was then administered on a voluntary basis.

After the FDA reviewed the vaccine again and approved it in December 2005, the Pentagon said in October 2006 that it would resume mandatory vaccinations for more than 200,000 troops.