ANYONE SEEKING weapons of destruction inside the United States may find it considerably easier after Sept. 13. Unless Congress wakes up and votes to do something about it, the federal ban on the manufacture of certain military-style assault weapons will expire that day, and the mad marketing of these dangerous firearms will resume across the homeland. Though lawmakers in both parties, and President Bush on alternate days, have looked at the polls and supported renewal of the ban, the gun-lobby-controlled leadership on Capitol Hill won't lift a finger unless prompted by the president. Mr. Bush, in turn, is said to be waiting for Congress to send him legislation.

It's a deadly runaround. This is no anti-gun- owner law. Ten years ago, when the ban was enacted, Rep. Henry J. Hyde (R-Ill.) explained his support for it: "I'm sensitive to the right of people to own a weapon. You have the right to defend yourself, especially in times when law and order seems to be very much under siege. But the proliferation of weapons whose only purpose is to kill a lot of people in a hurry seems to me not to be justified." Another prominent figure who lobbied for passage of the ban was former president Ronald Reagan.

Police officers whose lives are at risk on the streets have said time and again that assault weapons have no place in the mix of firearms for hunting or sport, that they pose a serious, unnecessary threat to law enforcement authorities. The gun lobby argues otherwise, claiming that semiautomatic assault weapons account for a small percentage of privately owned guns in America. So whose word should we take: the political mouthpieces of the National Rifle Association who promote the proliferation of anything with a trigger, or those who must deal with armed criminals, including snipers?

Opponents of the ban have still other absurd arguments for dropping the law. They say that the federal ban applies to only 19 weapons by name, and that copies are still out on the market; true, and all the more reason to improve the bill, not scrap it. As it stands, the federal law provides specific protection to 670 types of hunting rifles and shotguns currently being manufactured. Won't that do? Ah, but criminals will get assault weapons somewhere anyway, the gun peddlers say; sure, but is that a good reason to make it easier for them? What's so awful about life without assault weapons? Life with them is that much more vulnerable.

Mr. Bush need only give a forceful public cue to Congress to keep a ban in place. With the political conventions and elections this year, the days on Capitol Hill already are down to a precious few. Does the president care?