NO WONDER law enforcement authorities all around the country are beginning to question just whose side the National Rifle Association is on. For some time now, including an appearance on Capitol Hill last week, leaders of national police coalitions have been vigorously urging enactment of a modest protection against life-threatening quickie sales of handguns. All they seek is a seven-day waiting period for handgun purchases. They speak from more than a little experience too -- not only in combating crime but also in trying to stay alive on the job. Yet at every turn, the don't-give-an-inch propagandists of the NRA are busily distributing 25 convoluted excuses and countless fat campaign contributions for leaving things the way they are. Whose side will Congress take this time?

Public support for local police could make a difference. At last week's Senate subcommittee hearing on S.466, the waiting-period measure, representatives of most of the largest law enforcement organizations in the country made their case for the bill. Darrel Stephens, executive director of the Police Executive Forum, cast it as a matter of life and death:

"In 1985 handguns were the cause of 75 percent of all police officer deaths. Sadly, the numbers of those we remember during police memorial week grow each year. And what can we offer the survivors and friends of these law enforcement officers? We offer families a modest death benefit payment and sincere condolences. . . . We have an opportunity to keep those who are deemed to be of danger to our society or themselves from gaining easy access to handguns. This is an opportunity we should grasp."

Robert Scully, president of the National Association of Police Organizations, noted that national legislation is needed to establish some uniformity and to "eliminate 'forum-shopping' by criminals" who go to different states to buy handguns. Richard Boyd, national president of the Fraternal Order of Police -- the largest law enforcement organization in the country -- said the waiting period should be even longer, but if seven days "will save just one life, the life of a law enforcement officer or a citizen, then your work will be successful. . . . Until Congress is willing to stand up to the negative influence of these 'gun-is-god' advocates, who operate outside a hunting or sport shooting scope of interest, then safety legislation will be limited."

Still others, from the International Association of Chiefs of Police and Maryland State Police, spoke just as strongly for passage of the measure, which was introduced by Sen. Howard Metzenbaum and Rep. Edward F. Feighan and cosponsored by a growing list of members in both houses. Passage this year would come none too soon