Guess what doesn't get screened by airlines? Diplomatic pouches.

Despite the intense scrutiny of airline passengers and their bags since 9/11, potentially explosive gaps still exist.

Top among them, for some analysts, are diplomatic bags - the privileged cargo that is given special immunity.

Security experts worry that terrorists could exploit the status of diplomatic pouches, which are protected from being opened or detained in any way by the Vienna Convention of 1961. In the past, rogue countries and individuals have used such bags to transport drugs, arms, and cash - and even to smuggle people. That's because a diplomatic pouch can be a crate big enough to carry a large desk.

Some security experts say it's "only a matter of time" before terrorists aligned with a rogue nation - or a dissatisfied diplomatic employee in a friendly one - find a way to abuse the privilege. To prevent that, a growing number of security experts, along with some diplomatic scholars, are calling for the United States and the international community to revisit the sanctity of diplomatic pouches.

The issue is gaining ground as the International Civil Aviation Organization, which sets global aviation standards and best practices, prepares to review its security guidelines later this month.

"The US needs to take the lead in saying this is a vulnerability that needs to at least be explored," says aviation security analyst Andrew Thomas of the University of Akron in Ohio. "Putting our heads in the sand and acting like it's still 1961 in a post-9/11 environment is just not the way to go."

But advocates of more tabs on diplomatic pouches have found an unlikely opponent - the US government itself. The State Department has consistently opposed screening diplomatic bags. "We support [the Vienna Convention] as it stands," says spokesman Noel Clay. That's because it doesn't want American diplomatic pouches screened when they are used overseas. The department worries such a move could compromise the nation's international intelligence operations, Mr. Clay says.

That view is shared by many in the intelligence and foreign affairs communities. The logic is based on preserving the integrity of the Vienna Convention, says Alfred Rubin, professor emeritus of international law at Tufts University's Fletcher School in Medford, Mass. So, if the US insists on screening another country's diplomatic bags, then the US would be vulnerable to the same treatment.

"Then American diplomatic pouches can presumably be examined and X-rayed or opened by our Latin American and African neighbors, and America doesn't want that," says Professor Rubin. "But I do think we have to explore the options."

Advocates of diplomatic bag screening contend there are ways to protect diplomatic protocol and at the same time increase aviation security. For instance, countries could ferry sensitive documents and technology on their own military aircraft.

"Because of the historical record of state sponsorship of and complicity with terrorism, it's certainly something that should be discussed, especially when it comes to nonintrusive means of checking," says Prof. Robert Lieber of Georgetown University in Washington.

Since 9/11, the Canadian government has implemented a policy that allows it to request examination of a diplomatic pouch if it has reason to believe the contents are suspect. "If the process is unsuccessful, [they can] deny transportation of the bag," e-mailed Vanessa Vermette of Transport Canada in response to a question.

Asked if the US has a similar policy in place, Clay of the State Department did not answer directly with a yes or no. "Diplomatic pouches are inviolable under international accords," he says. "We expect that host countries will obey the uses of the diplomatic pouch and institute reasonable precautions to ensure they're used only as intended."

But there is a long history of diplomatic pouches not being used as intended. For instance, in 1984, British authorities found a former Nigerian government minister who'd been abducted and drugged in a large diplomatic crate bound for Nigeria from the Stansted Airport. Also in the crate was a man who was conscious and equipped with drugs and syringes, according to the the July 1985 issue of The American Journal of International Law. Three people were arrested and charged, one of whom claimed diplomatic immunity.

When asked recently if the issue of diplomatic bag screening should be revisited, Homeland Security Secretary Michael Chertoff demurred. "There's a lot of law and custom and treaty obligations with respect to this matter," he said at a Monitor breakfast. "We do want to be mindful of all kinds of threats, but we want to operate within the treaty obligations we have."