AN INGENIOUS NEW weapon against criminal bombing and terrorism has come under fire from groups who use old-fashioned, muzzle-loading firearms for sport and show. One might think that futuristic technology could hold its own against the flintlock, especially when better public protection is at stake. But the National Rifle Association has taken up the muzzle-loaders' banner, and the outcome in Congress is in doubt.

At issure is a plan that would make bombs less anonymous and much easier to trace. The system developed by federal agencies, industry representatives and other experts, involves tagging explosives by mixing in microscopic particles with identifying codes. The tiny tags, which could be found after a blast, would tell where and when that batch of explosives had been made. With those codes fed into existing record-keeping systems, investigators could track the materials at least through the last legal sale. Another kind of tag being developed would enable security forces to detect bombs more easily in letters, luggage and the like.

This is a noteworthy use of space-age technology with obvious public benefits. Identification tagging of dynamite and other cap-powered explosives is ready to start as soon as Congress approves the program. Within a year or two, the experts think they can perfect tagging of black and smokeless powders, which are often used in pipe bombs and have been involved in over one-fifth of the criminal "explosives incidents" reported to the FBI in recent years.

That's where the NRA comes in. Black and smokeless powders are also used, lawfully, by people who reenact historic battles, target-shoot with antique firearms and reproductions, or reload bullets at home. There are also the symphony orchestras that do full-blast renditions of the "1812 Overture." The orchestras have not been heard from, but the NRA certainly has. It argues that innocent hobbyists could be hurt - not by the tagging but by the record-keeping stores would have to do. Keeping track of powder packages need not be a major new chore, since everyone who buys even a pound of black or smokeless powder must already fill out a form. The NRA fears, though, that any new rules could some retailers to stop selling the powders. And it fears that powder-tagging could lead to ammunition-tagging or even - you guessed it - registration of guns.

Thus the gun group wants smokeless powder and sporting-grade black powder exempted from the tagging program now being advanced in the Senate and House. In our view, that would be a dangerous mistake. It would amount to putting on a different kind of tag - an invitation to criminals to make more bombs with these easily bought materials because they will be the hardest to trace. Instead of encouraging potential terrorists, Congress should spur the tagging program on. It wouldn't make it all that much harder to reenact the battle of Manassas - if that's your worry - or to perform the "1812 Overture." And it would almost certainly make it easier to combat criminals bent on terrorist bombings. Even the NRA ought to be in favor of that.