With the specter of bioterrorism, many people are casting about for ways to protect themselves and their families. The most commonly sought item is a gas mask. But experts warn the gas mask is overrated as a protective device against biological agents such as anthrax.

As the headlines continue to report cases of anthrax, sales of gas masks are booming. Established firms report a surge in sales, and new companies selling the masks pop up on the Internet every day. Ads tout the masks as protection against chemical and biological attack.

The problem, say experts, is that a gas mask offers a false sense of security. The Center for Civilian Biodefense at Johns Hopkins University flatly recommends that people not buy them. Clifford Mitchell, director of the occupational medicine residency program at the university's School of Public Health, says a gas mask is useless without advance warning of an attack. "In practice, no one would know when an actual release (of a biological agent) took place, so that, unless you had foreknowledge or had enough time so you had both foreknowledge and the opportunity to get and put on an effective gas mask, it really wouldn't serve much purpose," he said.

A gas mask - so named because it was originally designed to protect against poison gas in World War I - fits over at least the face and, in some cases, the entire head. Air is circulated through filters especially designed to keep the air pure and to keep out contaminants. However, unless a full body suit is worn in conjunction with the mask, it cannot protect against contamination through exposed skin.

Several purveyors of gas masks were asked for their reaction. Some refused to comment. But, when pressed, others - whose ads touted their masks as protection against biological agents - said they agree that a mask will not offer protection unless it is worn all the time. However, most ads on the Internet do not mention this fact.

Sean Stockmeyer of the Biologik Gas Mask Company in Nyack, New York, agrees with the experts' contention. But, he says, the mask may come in handy as the war on terrorism drags on. "This war on terrorism is not going to end overnight," he says. "So you might think of it as a like a fire extinguisher next to your stove. Hopefully, you're never going to need it. But you might just want to have it there in case. And maybe sometimes it wouldn't be effective because you've got too big of a grease fire or something like. And that's the same case with a mask. So it's a question of, do you want to roll the dice? And if you're not comfortable with that, then maybe get something for protection."

But, say experts, a mask must be professionally fitted to ensure a tight seal by the wearer - and that takes some training. Moreover, says Dr. Mitchell, a lot of masks being sold are old ones of dubious quality.

Dr. Mitchell believes the sellers of gas masks are trying to cash in on fear by offering false hope. "People are always going to try to market to peoples' fears. But I am concerned that people who are doing this - that is to say, the people who are selling the gas masks - are not doing people a service, in part because they are not telling them what kind of products that they're getting," Dr. Mitchell says. "And for the most part, most of these products would not be effective, even if they were used against small particles such as the anthrax bacillus."

Mr. Stockmeyer says he has been flooded with offers to buy lots of Cold War-era surplus masks from former Soviet bloc countries. But he says he only sells quality masks manufactured in Sweden in good working order which retail for at least $200.

Mr. Stockmeyer notes that, before the current scare, his firm was one of about 16 gas mask sellers one would find in a search on the Internet. Now, he says, the number is double or perhaps even triple that.

But, while he distances himself from the rush of dealers offering less than reliable products, he refuses to condemn them. "Well, you know, it's America. It's capitalism. I'm not going to denounce these people outright," he says.

Mr. Stockmeyer says buying a gas mask is a personal decision - and that consumers should educate themselves before making a purchase.