WHAT happened when the United States made it plain that further murder and rape in Bosnia would result in the bombing of Serbian positions and the arming of Bosnia defenders?
Suddenly the light of reason seemed to illuminate the Serbian leadership. The realization that conquest might have a high cost -- not only that uniformed killers would be killed, but that Serbian civilians would suffer -- caused the dictator in Belgrade to send word to his stooge within Bosnia to sign on the dotted line.
Skepticism is in order; shells still rain on Sarajevo, and it may be that this latest show of sweet reason is a subterfuge. Mr. Milosevic in Serbia and Mr. Karadzic in occupied Bosnia may be playing nice-war-criminal, tough-war-criminal with Lord Vance-Owen, pretending to make peace until the world relaxes.
If that delaying trick is tried, the best way to prove Western determination would be to turn out the lights in Belgrade -- to use air power to smash the utility infrastructure within Serbia in a way that would turn the people against the regime.
But let us assume that this time the instinct for duplicity is overcome by the driving force of fear. No excuses about local commanders not getting the word can be tolerated; the Serbian leadership should be required to execute the first artilleryman who orders a barrage after the cease-fire.
If the credible threat of U.S. military punishment at last stops the carnage, we should insist that the ancient device of a balance of power undergird the peace.
That means that the Muslim Bosnians must be armed to the level of the Serbs within Bosnia, or that the Serbs be disarmed down to the level of the Muslims. How? On a date certain, 100 tanks and 1,000 mobile mortars should be delivered to Bosnian forces unless the same number of Serbian tanks and mortars are turned over to peacekeepers. We have seen how imbalance invites war; give balance a chance.
On the assumption that our saber-rattling succeeds in silencing the guns while a patchwork nation is designed, what will we have learned?
First, in dealing with militias who enjoy bombarding civilians with impunity, we should recognize that fear of retribution works better than pleas for mercy. Serbian gunners may be savage, but they are not suicidal.
Next, in inducing a vulnerable conqueror to come to the negotiating table, nothing beats a direct, serious international effort to starve the war-making population. A blockade, which was meaningless in self-sufficient Iraq, hit home in oil-dependent Serbia, raising this question: Why were Messrs. Mitterrand, Kohl and Major, prattling about sanctions for a year, unwilling to impose an effective blockade a year ago?
Finally, in affecting Balkan public opinion, the imminent threat of the use of international force does not "rally the people, unify the nation, make the militants dominant, stiffen the tribal desire to get even" -- on the contrary, the likelihood of terrible retaliation scares hell out of most rational people, including all those uninterviewed Serbians who want to get on with their lives.
We are learning plenty about European leaders, who will risk the lives of soldiers on humanitarian missions but not in deterring messy aggression. Forget talk of Europeans "approving" air strikes while "vetoing" the U.S. plan to arm the Bosnians if the Serbs don't stop killing them; the European leaders have taken as their symbol a herd of sheep huddling under the wing of a superpower eagle.
And we are learning which of our own leaders to trust in the crunch. Senators Biden, Mitchell, Lugar and Dole have been stalwarts, in contrast to the quagmirization of the House behind Lee Hamilton and Speaker Foley.
In the Clinton administration, Al Gore, Les Aspin and Tony Lake are providing the backbone for intervention, with a stunning assist from Foggy Bottom below the Seventh Floor.
Barring a last-minute trick by the Serbian leaders to grab land before a cease-fire, President Clinton may be learning the lesson that at first eluded Presidents Roosevelt and Kennedy: The way to avert a war is to be demonstrably ready, willing and able to go to the brink of war.
Asked Sunday why that lifesaving resolve was not shown two months ago, Mr. Gore could only counter: "Or two years ago."
William Safire is a columnist for the New York Times.