Israel has a shortage of civilian gas masks, but you wouldn’t know it from walking down Manhattan’s St. Mark’s Place, where the masks are on sale in half a dozen stores for a mere $25 each.

The Israeli model 4A1 gas masks on display in the East Village — where storefront noodle shops bump up against vintage clothing stores — might not protect you from a chemical weapons attack. That’s because their protective filters have been removed and replaced with foot-long acrylic bongs meant for smoking marijuana.

Gas mask bongs, used by pot aficionados to intensify the drug’s impact, started flooding American head shops about a decade ago, some insiders say. That is roughly around the same time that the Israeli government recalled millions of masks it had distributed to civilians during the 2003 invasion of Iraq that the United States led.

It’s hard to say whether that timing is coincidental. But it is clear that the black gas masks with circular glass eyeholes, sold in American head shops, are authentic Israeli masks, down to the telltale rubber-triangle seal of Shalon Chemical Industries Ltd., the Tel Aviv-based company that makes all the civilian gas masks of Israel.

“They’re the real deal,” said Tony Lomeli, manager of RDD USA, a Los Angeles military surplus dealer that sells Israeli 4A1s for use as survival gear.

Though the masks themselves all look alike, the attached bongs vary. Some are long and straight, others end in a bubble. One mask-attached bong spotted in a display on St. Mark’s Place was shaped like a human face.

Though the appeal of the gas mask bongs may lie partially in their spooky aesthetic, they are valued mostly for the way they force smoke into the lungs. The seal around the user’s face, designed to keep out chemicals during an attack, locks in the marijuana smoke, forcing the smoker to inhale it all at once.

“It’s kind of a step above a bong,” said Rick Cusick, associate publisher of the marijuana-themed magazine High Times. “It makes for a slam dunk kind of thing.”

Cusick, 57, said that when he was young, smokers would hook up bongs to gas masks themselves. He said that the devices have become commercially available in only the past decade. One head shop clerk suggested that the 2007 movie “Knocked Up,” which featured a gas mask bong, likely contributed to their recent popularity.

Supply of the bong-mask combos doesn’t seem to be much of a problem. That’s not the case with functional, filter-fitted 4A1s, which are made to protect civilians from nuclear, chemical or biological attacks. Though the Israeli government has just finished distributing 4 million of the masks to its citizens, production is now stopped, according to a recent report in The Jerusalem Post, and budget shortfalls will mean that 40% of Israelis won’t receive 4A1s from the government.

Israel’s distribution of the 4A1s, meanwhile, has also caused something of a shortage of working masks in the United States, where doomsday predictions fuel purchases, according to Golan Friedman, marketing director of RDD USA. Lomeli said his company couldn’t get any more working masks from their Israel-based suppliers, although they are available online now.

“We cannot get a single one,” Lomeli said. “Whatever we have in stock, that’s it. When it’s gone, it’s gone.”

RDD USA’s functional masks with filters sell for $19.90 online.

According to Lomeli, the gas masks used to hook up with the bongs are likely surplus, sold by the Israeli government in bulk without filters. He said that they were probably among the masks recalled by the Israeli government beginning in 2006.

The sale of the gas mask bongs exists in something of a legal gray area. Merchants in New York are protected by an interpretation of state law that forces prosecutors attempting to prove a drug paraphernalia case to show that a device in question is intended for use with illegal drugs, a high legal bar. As long as the gas mask bongs are marketed for use with tobacco, the sellers and wholesalers are safe under state laws, experts say.

Federal laws are tougher. If someone is accused in federal court of selling drug paraphernalia, prosecutors need to show only that the items are meant for use with illegal drugs, not that the seller specifically intended them for illegal use. According to Robert Vaughn, a Tennessee attorney who sits on the board of the marijuana legalization advocacy group NORML, federal charges against paraphernalia vendors are very hard to defend. The sale of drug paraphernalia is a felony under federal law and carries a possible prison sentence of three years.

Still, prosecutions are relatively rare. “In all candor, they can’t prosecute everybody,” Vaughn said. “So what are the statistical odds it will be you and not me?”

Contact Josh Nathan-Kazis at nathankazis@forward.com or on Twitter @joshnathankazis