AYLOR, Mich.

A guard at the entrance to the convention hall politely stopped me. "You've got to check your guns here," he explained.

By lucky coincidence, I wasn't carrying a concealed handgun. But the Michigan Gun & Knife Show, held here over the weekend, was the place to buy any kind of pistol and lots more: huge .50-caliber semiautomatic rifles, fuse wire, Confederate flags and 75-round clips for an AK-47 in case I wanted to pursue moose that lacked the sense to flee if I missed the first 74 times. Plus instruction manuals for converting semiautomatic rifles into machine guns and, for $10, "How to Build Your Own Bazooka."

Gun show bumper stickers are big on machismo: "I just got a gun for my wife — It's the best trade I ever made" and "Warning: Driver only carries $20 worth of ammunition."

As I tried the feel of a used $129.95 Polish assault rifle with a handy bayonet, the seller beamed. "That's a powerful gun," he said. "It's the only one I know that can put a round through bulletproof glass."

Hmmmm. That did make it a useful sporting weapon, if ever I anticipated hunting deer as they traveled in armored limousines.

These gun shows are incredibly common — there are 4,500 of them a year in the United States — and constitute one loophole in the war on terrorism that the Bush administration refuses to plug.

Instant background checks are normally required before a gun purchase. This check system has stopped 690,000 sales of guns to people with felony convictions. But the background checks are not required when unlicensed dealers sell at gun shows.

The upshot is that at gun shows, criminals or terrorists can buy an arsenal without even showing an ID. Here in Michigan, for example, a member of Hezbollah, Ali Boumelhem, was convicted last year of buying weapons at gun shows to ship to Lebanon.

Years ago I was held at machine-gunpoint one night in Beirut, and it seemed the gun capital of the world. So it's unnerving to learn that frustrated Lebanese terrorists come to America for weaponry by taking advantage of our lax gun rules.

I found three other recent examples of people with terrorist connections — an Irishman and two Pakistanis — also shopping for weapons at American gun shows. Of course this isn't primarily an issue of international terrorism, but rather an urgent public health crisis: guns kill one American every 20 minutes. Even since Sept. 10, six times as many Americans have died from guns as from international terrorism.

That isn't likely to change much, for 48 percent of American voters have guns in their homes — and ownership of firearms rises with income and education. But we can muster a political consensus to take limited steps like closing the gun show loophole to save lives and hamper criminals and terrorists.

Eighteen states have already moved to reduce the loophole, and the burden of federal action would be minimal. At this Michigan show, sales were permitted only after a background check, yet no one seemed terribly inconvenienced or went postal. When I pressed one dealer on whether the instant checks were a burden, he shrugged and launched on a riff about a more vexing concern: a young man who had recently rented a gun to commit suicide.

"Can you believe it?" he complained. "He was too cheap even to buy the gun!"

During a presidential debate with Al Gore, George W. Bush said: "I support instant background checks at gun shows." Even John Ashcroft, who may well have been born clutching a handgun in his tiny pink fingers, told a Senate subcommittee, "This administration does support closing the gun show loophole."

But President Bush refuses to put his administration where his mouth is. He has not endorsed either of the bills that would begin to close the loophole. (One of them, a compromise sponsored by Senators John McCain and Joseph Lieberman, is that rarity, a major gun safety bill with a Republican sponsor.)

President Bush prides himself on his willingness to do whatever it takes to fight terrorism — lock up zillions of Arab men, introduce military tribunals, invade Afghanistan and Iraq. If terrorists were buying weapons at these kinds of gun shows in small foreign countries, we might try bombing them. So what about closing America's own gun show loophole?