As the deadline drew closer last week, the West was at pains to maintain solidarity. It wasn’t easy. At one point, NATO’s ultimatum began to look negotiable, faltering on a definition of U.N. “control” of weapons. The Serbs balked at giving up their guns, insisting that the Muslims first withdraw their infantry. Then, in rolled the Russians, pulling off a surprise diplomatic coup. Only four days short of the deadline, they persuaded the Bosnian Serbs to start moving their big guns and tanks out of the exclusion zone (map) – in exchange for a Russian troop presence around Sarajevo. That deal gave the Serbs a face-saving excuse to retreat, and made airstrikes less likely. Clinton welcomed Moscow’s participation. But he continued to prepare for battle, notifying Congress about possible military action, explaining the mission to the American public and sending his top military advisers to the Aviano air base in Italy to sign off on NATO’s final attack plans. “Our actions,” the president warned, “will be determined by one thing, the facts on the ground.”

At the end of the week, those facts were still sketchy. Cloud cover over Sarajevo, where snow had been falling most of the week, made NATO reconnaissance flights all but useless. U.N. brass in the capital continued to claim an exodus of Serbian heavy weaponry – and White House officials expressed cautious optimism. But the Bosnian government charged that, far from relinquishing their weapons, the Serbs were moving in new artillery to positions from which they’d carried out the 22-month siege. A NEWSWEEK reporter traveling on the steep and icy roads around Mount Trebevic, the Serbs’ largest gun emplacement southeast of Sarajevo, saw no evidence of withdrawal. At one site stood a truckmounted mortar, the same 120-mm type that had killed 68 civilians in Markale market. Bosnian Serb soldiers guarding the equipment claimed they were pulling back; but observers familiar with the area said the mortar had been parked there for days. Asked how the retreat was proceeding, a French peacekeeper monitoring the situation said, “Briefing the press is not part of my mission.”

Crossed signals threatened to undermine the NATO ultimatum early in the week. The U.N. commander in Bosnia, Lt. Gen. Sir Michael Rose, got out in front of NATO by suggesting that the Serbs didn’t have to surrender their weapons so long as U.N. forces could keep an eye on them through electronic surveillance. Then came the ultimate challenge to Western resolve. “The 10-day ultimatum is a NATO ultimatum, it is not our ultimatum,” said U.N. spokesman Lt. Col. Bill Aikman.

The White House paid scant attention to the growing schism between the United Nations and NATO – until national-security adviser Anthony Lake picked up the newspapers on Wednesday morning. The new definitions of weapons control didn’t sound right to him. He consulted with Secretary of State Warren Christopher, Defense Secretary William Perry and Joint Chiefs Chairman Gen. John Shalikashvili. They all agreed to spell out unambiguously the strict terms of the ultimatum. Shalikashvili sent word to Adm. Jeremy Boorda, NATO’s Southern Europe commander, to “straighten it out,” according to a senior White House official. Boorda had already laid the groundwork. At a meeting in Zagreb, Croatia, NEWSWEEK has learned, Boorda put on a slide show for Rose, X-ing on the projection screen scenarios in which Serbian artillery would be considered “targets” for NATO strike aircraft. Rose later changed his tune: “What I mean by “under U.N. control,’ and it’s been said many times now, is this: if any party tries to make use of the weapons that are under control, they will have to use force to get to them.”

Getting Rose under control was one thing; dealing with Russian freelancing was another. Just as NATO and the United Nations closed ranks, President Boris Yeltsin intervened. He made the Bosnian Serbs an irresistible offer: withdraw tanks and artillery in compliance with the NATO ultimatum, and 800 Russian troops, under U.N. command, would take up positions around Sarajevo. Deputy Foreign Minister Vitaly Churkin, who brokered the agreement, called Yeltsin’s move “a brilliant idea” for solving the Bosnian crisis. “I know there are some people in NATO who are advocating the strategy “strike and [then] negotiate’,” he said. “In Bosnia and Herzegovina . . . you can have either negotiations or an all-out war.”

Churkin’s comments sounded like a slap at the West – but were in fact aimed at strengthening Yeltsin’s shaky position at home. “An airstrike on Bosnia could cause a political explosion in Russia.” says Aleksandr Konovalov, an analyst at Moscow’s Institute for U.S.A. and Canada Studies. Since the December elections, hard-line nationalists have accused the Foreign Ministry of betraying Russia’s traditional allies, the Serbs. Konovalov speculates that if Yeltsin had failed to act and had acceded to Western bombing, the lower house in Parliament would have initiated a vote of no confidence in the government. Yeltsin had recently made no secret of his irritation at being excluded from NATO’s plans. The ultimatum presented him with three stark choices: back the West and risk a fight at home; support the Bosnian Serbs and provoke a major confrontation with Washington, or defuse the crisis through negotiation.

Washington had some advance warning of the Russian initiative. Clinton had encouraged Yeltsin to pressure, the Serbs, asking him on Feb. 11 for “as much help as we could get,” as one administration official put it. In a “frank, direct and personal” letter to the president last week, NEWSWEEK has learned, Yeltsin asked Clinton to be absolutely clear about what steps the Serbs had to take to comply with NATO’s ultimatum. The implication: that Moscow would endorse that outcome. “This is not altruism,” says a senior administration official. “It’s in everyone’s interest to stop the war.” But to win the agreement of Bosnian Serb leader Radovan Karadzic, Churkin had to promise a military presence in Sayajevo. This did take the White House by surprise – and shocked the Russian Defense Ministry, still smarting from its disastrous experience in Afghanistan.

While a team from the Russian General Staff prepared to assess the situation in Sarajevo, NATO defense leaders gathered in Italy just hours before the deadline expired. They weren’t just talking bombs. They were also discussing what-next scenarios. If a cease-fire held in Sarajevo – and if the capital were soon placed under U.N. control – could a similar approach work in other besieged enclaves throughout Bosnia? General Rose had suggested the towns of Mostar, Gornji Vakuf, Vitez and Maglaj; Christopher had mentioned Srebrenica and the Tuzla airport as natural candidates.

But large problems lie ahead, with battles raging throughout Bosnia and control of 15 towns in dispute. Will the international community, now committed to Sarajevo, try to establish “peace by piece,” as one senior Pentagon official put it? Deadlines, even if backed by the threat of force, might begin to lose their effect. There is also the colossal challenge of policing each settlement, town by town. The United States, which has no ground troops in Bosnia, will be under increasing pressure to live up to its promise to contribute peacekeepers particularly now that Russia has agreed to send soldiers. Defining America’s role in a Bosnian peace will be even tougher than scaring the Serbs into ending the war.