THE TREASURY DEPARTMENTS Alcohol, Tobacco and Firearms Bureay has, shall we say, come under fire from the National Rifle Association and congressional opponents of gun-control laws. Their target is a set of regulations proposed by ATF that they claim would create, in NRA's words, "a massive system of centralized national firearms registration" with "no specific congressional authority."

ATF is doing nothing of the sort. The agency is simply trying, at long last, to crack down on the vast, nationwide illegal traffic in guns. Under the proposed rules, every new firearm, including future imports, would have to bear a unique serial number. Licensed manufacturers, importers and dealers would have to file quarterly reports on the disposition of each firearm they make or handle. Finally, every theft or loss of a firearm in commercial channels would have to be reported at once.

We emphasize "commercial channels" because the rules would not require any reporting or registration by individual owner of guns. While reporting that a given firearm had been sold, dealers would not have to tell Washington the buyer's identity. Dealers would have to keep that information, as they do now - and ATF agents could inspect those records during business hours, as they may now. The rules governing legitimate firearms purchases and possessions would not be changed.

What would be changed - and in our view greatly improved - is the ability of officials to trace the thousands of firearms used in crimes. Last year ATF conducted a record 62,498 trace efforts, many at the request of state or local agencies, with success in 55 percent of the cases. The process now requires separate inquiries to manufacturers, wholesalers and retailers. If future commercial records are centralized and computerized, the history of illegally used guns can be reconstructed much more quickly and easily.

Beyond that, ATF could gain a much clearer picture of the whole firearms business. Officials have documented some well-traveled channels through which guns move from legitimate commerce to crime. ATF found last year, for instance, that over half of the firearms confiscated by the District of Columbia police came from Maryland or Virginia. Mississippi seemed to be the main out-of-state source for guns seized by Chicago's police. But how do the firearms get to Maryland, Virginia or Mississippi? Past administrations have not pressed the industry for information. The new system would enable ATF to find out - for the first time - precisely how many firearms are being made, where those weapons go in commerce, and where they leave commercial channels by means other than documented sales.

Finally, what about the charge that ATF is excedding its authority? That's nonsense. In the 1968 Gun Control Act, Congress specially required licensed firearms manufacturers, importers, dealers and colectors "to maintain such records" and "submit to the Secretary [of the Treasury] such reports and information with respect to such records and the contents thereof as he may be regulation prescribe.? (That's in Section 923(g) of Title 18, U.S. Code, in case you want to look it up.) So the NRA is way off target. Congress should encourage, not hamper, ATF's new effort to enforce the laws.