Saying American soldiers should not be used as "guinea pigs for experimental drugs," a federal judge Monday ordered the Pentagon to stop mandatory anthrax vaccinations started in 1998.

U.S. District Judge Emmet G. Sullivan said he was convinced by plaintiffs in a class action suit that the vaccine is experimental and being "used for an unapproved purpose" -- that is, for exposure to airborne anthrax (search) as well as exposure through the skin.

• Raw Data: Doe v. Rumsfeld (FindLaw pdf)

Officials at the Defense Department and Food and Drug Administration (searchsaid they had not seen the ruling and had no immediate comment. But the federal government has long maintained that the licensed vaccine is safe, is not experimental and can be used for protection against anthrax inhaled or absorbed through the skin.

More than 900,000 servicemen and women have received the shots, among the millions of doses of various vaccines administered annually to protect troops against disease and bioterror threats. Hundreds of service members have been punished or discharged for refusing them, according to the Pentagon.

"The women and men of our armed forces put their lives on the line every day to preserve and safeguard the freedoms that all Americans cherish and enjoy," Sullivan said in Monday's 34-page ruling.

"Absent an informed consent or presidential waiver, the United States cannot demand that members of the armed forces also serve as guinea pigs for experimental drugs," Sullivan said.

In granting the preliminary injunction, Sullivan ordered the government to file responses by Jan. 30.

Anthrax is a naturally occurring bacterium that typically affects sheep and cattle. When inhaled, dry anthrax spores can be deadly to humans.

The federal government approved the vaccine three decades ago. But plaintiffs -- unidentified active duty, National Guard and civilian defense employees -- say the license was only for exposure through the skin, and that it may not be safe.

Sullivan's ruling said the label on the vaccine does not specify which method of anthrax exposure it protects against.

He cited a 1998 law prohibiting the use of new drugs or those unapproved for their intended use unless people being given the drug consent to its use or the president waives the consent requirement. Congress passed the law amid fears that the use of such drugs may have led to unexplained illnesses -- which have come to be known as Gulf War Syndrome (search-- among veterans of the 1991 Persian Gulf War.

The anthrax vaccine itself has been approved since the 1970s and used regularly to protect veterinarians and scientists working with anthrax.

Believing Iraq and other nations had produced anthrax weapons, former Secretary of Defense William Cohen in 1997 ordered the armed forces immunized.

While the government does not recommend vaccinating the general public, it says the vaccine overall is very safe, with rare severe side effects such as dangerous allergic reactions.

But hundreds of military personnel have refused the shots, worried they could be connected to complaints of chronic fatigue, memory loss and other problems.

A leaflet inserted with the product, which originally stated that adverse reaction occurred in 0.2 percent of cases, was recently revised to reflect a rate between 5 percent and 35 percent, the ruling said. It said there have been at least six deaths linked to the vaccine.

The 0.2 percent rate came from an earlier government report that there were only 105 serious reactions in over 830,000 recipients, the ruling said without giving details.

The program was started to vaccinate all 2.4 million members of the active and reserve military, but was radically reduced after factory violations by the nation's sole vaccine manufacturer resulted in dwindling supplies.

The FDA cleared Lansing, Mich.-based BioPort's manufacturing plant in January of 2002 to produce the vaccine and to resume shipments.

After a three-month study considering the new domestic need, previous supply problems and other issues, the Pentagon decided to give the shots only to troops, essential civilians and contractors who are assigned for more than 15 days to "higher threat" areas of the world.

Officials declined to identify those areas. Nor would they say how many troops would be given the vaccine. It is likely that these areas include the Persian Gulf and the Korean peninsula.