An Air Force nurse has been punished by superiors for writing a letter to the military newspaper Stars and Stripes questioning the safety and effectiveness of anthrax inoculations being administered to all U.S. troops.

Capt. Debra J. Egan, a pediatric specialist, raised concerns about the vaccine's possible side effects, its impact on fertility and its usefulness against airborne anthrax spores. Pentagon authorities dismissed her fears as groundless, noting that the vaccine has been licensed by the Food and Drug Administration for nearly 30 years and used by many civilians as well as military special forces.

But even if Egan's scientific position is weak, her case raises questions about free speech in the military and highlights the extreme sensitivity of the Pentagon to the small but steadily growing number of troops who refuse the anthrax vaccine.

"The Air Force's handling of this case suggests a climate in which commanders can almost crack down on critical letter writers at will," Bill Monroe, the ombudsman for Stars and Stripes, wrote in a recent column supporting Egan.

After her letter, Egan, 45, received a stern written rebuke from her squadron commander. A negative comment also was added to her performance report, reducing her chances for promotion next year. And she was denied a commendation medal after a four-year tour in Okinawa that she said was marked by otherwise flawless evaluations.

"People need to know it's not safe to write letters and express your opinion unless it's the same opinion that the Air Force has," Egan said in a phone interview. "I guess if they want us to have an opinion, they'll give it to us."

Air Force attorneys last week defended the censure, saying Egan's mistake was using her military position to buttress her criticism.

"It's not what they say, but how they use their office or position to support what they are saying," said Gordon Wilder, an Air Force counsel.

"If she had spoken purely as a private citizen," added Col. Jack Rives, another Air Force lawyer, "she would have been free to say almost anything she wanted."

The inoculation plan is the first attempt to protect the entire U.S. military against a germ warfare agent. Since it was announced in December 1997, the program has encountered little outright resistance, but it has engendered widespread unease in the ranks about the vaccine's effects. Out of 318,000 troops ordered inoculated so far, more than 200 have refused the shots--and have been discharged from the military as a result.

Pentagon authorities and many independent experts insist the vaccine is safe and effective. But in her Nov. 5 letter, Egan expressed doubts that service members were being adequately informed about the vaccine's "risks and possible side effects."

Citing a vaccine product information leaflet she said she read on a Web site, Egan asserted that no scientific studies have determined whether the vaccine causes cancer or affects fertility. She said a principal chemical component of the vaccine, formaldehyde, is not approved by the government for human consumption and is a carcinogen. She also wrote that there have been no studies confirming the vaccine's effectiveness against inhaled anthrax spores, as opposed to anthrax contracted through the skin.

"If only few object to this experiment, then it will continue, and we will all take the risk," Egan concluded. "But if numerous informed individuals ask the questions, maybe we can make a difference."

That final statement incensed Air Force authorities, who read it as bordering on a call for insurrection.

Egan did not give her rank in signing the letter, but she identified herself in the text as a health care professional and listed her address as Kadena Air Base in Okinawa.

"She was well-known to the audience there," said Wilder, the Air Force counsel. Egan's commanders were concerned that "a readily identifiable officer" could be perceived as "telling people to act in concert to do away with" the vaccination program, Wilder added.

Retribution was swift. Egan's medical squadron commander, Lt. Col. Dan R. Hansen, issued a critical "letter of counseling," while two other military officials wrote Stars and Stripes contending that Egan's information was wrong or insignificant.

"As an Air Force officer, it is your job to promote and support the decisions of your superior officers regardless of your personal beliefs," Hansen told Egan. "Any need to clarify your concerns must be made through your chain of command and not through the editorial page of a newspaper."

Egan also received an officer performance evaluation that included a negative statement recommending mentoring to improve her leadership abilities. Transferred to California's Travis Air Force Base in June, the military nurse remains shell-shocked by the uproar, noting that she had written three earlier letters to the editor on other subjects without drawing a peep from superiors.

"I thought I had free speech," Egan said. "I thought I could express my opinion and urge service members to think through the anthrax vaccine and be sure they were well aware of the facts. I felt I had a moral obligation as a health care professional to express that."