WITH the clock ticking toward Sunday's deadline for the withdrawal of Bosnian Serb artillery from around Sarajevo, United States officials will work hard this week to try to keep Serbs from interpreting NATO airstrike threats as yet more empty bluster.
Over the weekend, Clinton administration spokesmen warned that NATO will accept nothing less than full and complete control of the heavy weapons that have pounded Sarajevo for years.
``All the forces are coming together to make sure that particular ultimatum stays in place,'' said US Ambassador to the United Nations Madeleine Albright on a television talk show.
In the face of an uncertain Serb response, some US experts continued to warn that the US and its NATO allies need to think through their response beyond a first-round spasm of bombing.
If Serbs attack UN peacekeepers or widen infantry attacks in response to airstrikes, NATO must be ``psychologically prepared'' to intensify its use of force, warned Sen. Sam Nunn (D) of Georgia. That would likely mean a second step of bombing targets outside of artillery sites surrounding Sarajevo.
If NATO is not willing to attack a wider set of targets, then it is ``really not prepared to take the first step,'' Senator Nunn said.
New US Defense Secretary William Perry has said that the US, for its part, is studying this possibility. With precision-strike F-15E aircraft added to the 160 to 200 planes in the region, NATO's power has been bolstered for relatively heavy-duty attacks.
NATO equipment in the region is now capable of pinpointing the origin of fired shells within seconds, Mr. Perry said. Aircraft can pounce on the target within minutes.
Still, the tough talk of airstrikes coming from the US has not been entirely matched by UN forces in the region. Creating some confusion over split aims, UN peacekeepers in Sarajevo have said that the Serbs may not need to hand over their artillery tubes to UN control.
Simple monitoring with ground-based artillery-tracking radar might be enough to consider the Serb guns sequestered, suggested some UN forces. ``The 10-day ultimatum is a NATO ultimatum; it is not our ultimatum,'' said Lt. Col. Bill Aikman, a UN Protection Force spokesman in Sarajevo.
The UN's position on the issue is important, since UN officials say the responsibility for actually calling in airstrikes is theirs.
NATO's newly tough line on the issue, however, will be difficult for both the Serbs and the UN to ignore. A sudden convergence of aims between France and the US has dragged reluctant allies much closer to actual use of force than at any time yet in the prolonged Balkans crisis.
After last weekend's tragic shelling of a Sarajevo market, the French have come around to the US view that tougher military actions are needed to end the suffering. In return, the US has accepted the French view that Bosnian Muslims must be pressed to accept some sort of negotiated end to the fighting, despite losing much of their land to Bosnian Serb aggression.
Sudden US hawkish talk marks a complete turnaround after months of mumbling on the Bosnia issue. US officials used to say that while the killing there was horrible, there were no direct US interests that called for involvement. The lesson of Somalia - where a dozen US combat fatalities will essentially result in the pullout of US troops - was foremost in their minds.
Almost half of the US public now supports some sort of military action in Bosnia. Whether that support will last, as memory of the market attack fades, is another question.
Clinton officials also came to see that months of empty threats were greatly affecting NATO credibility. If the alliance could not agree on a unified plan of action when fighting erupted in its own back yard, how would it react to more serious instability in Russia's so-called ``near abroad?''
So as US officials now rattle the possibility of airstrikes they appear to have truly crossed a threshold of seriousness. To back down now, if Serb shelling of Sarajevo does not end, would be to invite not just a credibility problem for NATO, but a crisis of unity among its members.
Whether the Bosnian Serbs will be able to give up just enough to avoid punishment, while still maintaining their grip on the city, is another question. If nothing else, the citizens of Sarajevo are likely to see the shelling end.
Sen. Bob Dole (R) of Kansas, a critic of the Clinton administration's slowness in urging airstrikes, said Sunday: ``It seems to me we've reached that point where if we have any credibility left, which isn't a great deal, it would be all gone if we didn't follow through.''