ONE OF THE MOST revealing studies of the civilian trade in firearms has just been completed by the Police Foundation, after two years of work, and its implications are grim for those who seek to stem the tide of illegal weapons flowing through the streets of our cities. The most chilling and disturbing of all the report's conclusions are that as many as 275,000 guns are stolen a year in this country.

Firearms that start out in the hands of law-abiding citizens may now theoretically supply enough weapons through thefts to commit all the firearms crimes in the U.S. each year, assuming that each firearm is used to commit only one crime.

The report thus suggests a stupefying spiral. The guns the good guys buy to protect themsslves against the bad guys are stolen by the bad guys, who then turn them on the good guys, which makes the good guys all the more apprehensive, so they buy more guns, which in turn enriches the supply from which the bad guys acquire an ever-expanding arsenal. Is there no way to interrupt this domestic arms race? The report suggests that one way might be found in the role in the gun traffic of the Alcohol, Tobacco and Firearms bureau of the Department of the Treasury.

As its very name suggests, firearms are not the ATF's foremost priority. In addition to running down moonshine and blackmarket cigarettes, ATF personnel are often used to handle the overload that falls on the Secret Service to protect political candidates and visiting dignitaries.

The agency is undermanned and underfunded. Still, it is the federal agency responsible for the enforcement of the Gun Control Act of 1968, which is the only law available at the federal level to stem the interstate traffic in guns.

As matters now stand, ATF is not making much of a showing. But as the Police Foundation report makes abundantly clear, the administration could give the agency far more clout in the field if it so chose, and Congress could add the money needed to hire more people. Those two efforts would not in and of themselves stop the massive traffic in illegal handguns, but they could have some impact. Since Congress has been reluctant to provide more potent legislation, ATF should be given the prod toward excellence that it has not had up to now.

ATF is pictured in the Police Foundation report as fearful of pushing the power it has lest the manufacturers of guns be "inconvenienced" by ATF's demands for information. The information that would help keep track of all those stolen guns is within the power of ATF to require by regulation, the Police Foundation says, but ATF officials candidly conclude that requiring the information would be "theoretically possible, but politically impossible." As a result, ATF restricts itself to that information the major manufacturers are willing to provide. And that isn't much.

That is not to say that there isn't a great deal to be learned about the commerce that feeds our national gun mania. An example: For years, AFT's research has tended to implicate the "Saturday Night Special," or cheap handgun, in most street crime. The Police Foundation report devastates that claim with evidence that the products of two leading "quality" gun makers, Smiths and Wesson and Colt, account for nearly a fourth of all the handguns confiscated by police. This is almost uniformly the case in every part of the country, suggesting that the handgun trade is a tightly integrated market with national patterns of distributions.

Given those facts, you would think ATF would be in a position to report on such essentials as how many weapons each manufacturer makes and tell you with some precision where those weapons go in commerce. Not so. ATF's fear of "inconveniencing" the manufacturers and their powerful protectors in the gun lobby and in Congress results in a shroud being pulled over this deadly marketplace whose activities so profoundly affect urban life. If the Carter administration wishes to get a grip on at least some part of the problem of handgun proliferation, making ATF an effective regulator of the gun industry would not be a bad place to start.