As the U.S. gears up for a potential confrontation with Iraq, the U.S. Food and Drug Administration has halted use of older lots of the military's anthrax vaccine, and officials acknowledge that the vaccine is riskier than once thought.

In August, the FDA acknowledged that the vaccine manufacturer's license needed to be updated. That was seven months after the agency ordered that new warnings for consumers be included in the vaccine's insert package. It said the vaccine could harm people with immunity disorders, could cause a host of serious long-term adverse reactions and could already be responsible for six deaths and a number of birth defects.

The warnings, developed from complaints by military vaccine users since 1998, state that adverse reactions are expected in 5 percent to 35 percent of people who take the injection. That compares with the previous expected rate of 0.2 percent, established many years ago.

But the label represents more than a simple warning. It is tantamount to an FDA admission of a licensing problem that began in 1985 and remains unresolved today.

The Department of Defense has said it is developing a new anthrax vaccine to respond to the concerns connected to the one in use now, but it asserts that the vaccine is both safe and effective.

In 1985, the FDA began reviewing the anthrax vaccine's manufacturing process to ensure it complied with federal rules for drugs. Recently, the FDA conceded to two Connecticut Air Force Reserve pilots that the review was never completed. The FDA told Maj. Russell Dingle and Maj. Thomas Rempfer that it would accomplish this, but didn't set a deadline to do so.

Dingle, of East Hartford, and Rempfer, of Suffield, who jointly filed a citizen petition with the FDA and a federal lawsuit against the manufacturer challenging the vaccine, said they don't truly expect the FDA to review the process again. That is because if the agency does, they said, it will have to stop licensing the drug. The central problem is that the drug was never properly tested, said the two pilots, who have been researching the drug since they were ordered to take it while in the Air National Guard in 1998.

Manufacturers apply for drug licenses with the FDA after testing their products on volunteers. The FDA reviews the tests, the vaccine's safety and effectiveness and the manufacturing process before approving the license to manufacture the vaccine.

In 1970, Merck, a pharmaceutical company, obtained the initial federal license to produce the anthrax vaccine. It eventually stopped manufacturing the drug.

In the 1970s and 1980s, the Pentagon began sponsoring the manufacturing of the vaccine through the state of Michigan's health department. It used the old Merck testing data, collected from volunteers working in sheep wool mills, to justify the safety and effectiveness of the Michigan-manufactured vaccine.

Because the FDA never properly scrutinized this testing, and because the manufacturing process was changed in 1990, said Dingle and Rempfer, the drug simply is not properly licensed.

And its latest adverse reaction rate, they said, shows the vaccine is indeed different from the one tested by Merck.

In 1998, BioPort Corp. of Lansing, Mich., purchased the state of Michigan's manufacturing operation and all of its vaccine, then used it to inoculate the first 500,000 of the 2.4 million service members ordered to take it. In the meantime, BioPort sought approval to produce its own new batches of the vaccine.

In January, the FDA approved BioPort's facilities and its vaccine manufacturing processes after four years of failed federal inspections and infusion of millions of more taxpayer dollars for plant improvements.

As a result of Dingle's and Rempfer's challenge to the vaccine, the FDA said only the new BioPort batches can be used. In June, the Pentagon had ordered both the old and BioPort's newer vaccine to be used, in high threat areas only.

Because of the FDA's concession that the old vaccine, manufactured by the state of Michigan and sold by BioPort, was not properly tested for safety and effectiveness, Rempfer and Dingle said, the Defense Department should now promptly pardon hundreds of service members punished for refusing to be inoculated with that vaccine. They insist the department should also properly care for the hundreds who became ill from adverse effects of the vaccine.