ZAGREB, CROATIA — HALTING Europe's bloodiest conflict since World War II is tantalizingly close, observers say. But tens of thousands of US ground troops soon may be deployed in Bosnia.
Over the next pivotal week, US diplomats, NATO pilots, and Serbian President Slobodan Milosevic will either lay the foundation for a lasting peace in Bosnia that will place a few American lives at risk or fuel another round of fighting likely to promote a potentially bloody US-led UN withdrawal.
The stakes for President Clinton and thousands of American troops will be enormous. If the NATO bombing-backed US peace plan fails, as many as 25,000 US troops may have to lead a UN withdrawal from Bosnia. They also could be responsible for arming or training the Muslim-led Bosnian Army.
If peace talks backed by force succeed, as many as 10,000 US troops may be deployed to enforce a partition of the country.
Either way, the use of heavy US-led NATO airstrikes against the Bosnian Serbs has resulted in the Americanization of the war, something Clinton administration officials say they have been desperately trying to avoid.
''What Americans better understand is that the American phase of this is just beginning,'' says Greg Vuksic, an aide to Sen. Pete Domenici (R) of New Mexico and a former US military attache in Belgrade. ''This is either going to be another Beirut [with the US backing one side] or a Korea, with US troops in place for years to come.''
Following a brutal and massive wave of ''ethnic cleansing'' by the Croatian government and the Bosnian Serbs this summer, the broad outlines of a US-backed tacit partition of Bosnia into three ethnically pure ministates has suddenly become plausible. But whether the sudden Western unity and Serb disunity that have raised hopes for peace will remain is unclear.
Watching current events
Key leaders and developments to watch with anticipation or dread, according to Mr. Vuksic and other analysts, include:
* Mr. Clinton: The president, fearing an election-year foreign-policy Achilles heel, has focused the energies of the administration on Bosnia. But quick results are unlikely, and the Bosnian Serbs are hoping the latest US-led flare-up of Western resolve will fade with time. Meanwhile, the concept of sending as many as 10,000 US ground troops to enforce a peace deal just before an election may lead Clinton to back away from a final peace deal.
* Sen. Bob Dole: The Republican presidential front-runner from Kansas, who controls whether the US Congress votes to unilaterally lift the UN arms embargo on the Bosnian government, can scuttle or speed up a peace deal. If Dole, who has promised to delay the vote as long as airstrikes continue, can have the Senate override a Clinton veto, European governments who oppose a lifting of the embargo could withdraw their already tenuous support for airstrikes. Any move to lift the embargo is also likely to spark protests and fuel suspicions among the Serbs, and more importantly, Russia, which supports the Serbs.
* Slobodan Milosevic: The Serbian president holds the most cards and is the key to peace in the region. Milosevic, once called a war criminal by former US Secretary of State Lawrence Eagleburger, won a year-long political duel with ultranationalist Bosnian Serb leader Radovan Karadzic last week.
Milosevic will now have final say over whether the Bosnian Serbs must accept a peace plan, but whether he is willing to satisfy the Bosnian government by taking a mostly rural 49 percent chunk of Bosnia is unclear. Milosevic, whose nationalist rhetoric fueled the break-up of the former Yugoslavia in 1991, also appears unlikely to satisfy the Croatian government demands that he also give up Eastern Slavonia, the last rebel Serb-held part of Croatia.
''I don't believe he has given up on a 'Greater Serbia,' '' says Dan Nelson, an international relations professor at Old Dominion University in Norfolk, Va., and Balkans specialist. ''I think he's just running scared at the moment.''
* Sarajevo: The Bosnian capital is a simple, but crucial, early litmus test. The reestablishment of the 12.5 mile heavy-weapons exclusion zone, reopening of the Sarajevo airport, and other siege-breaking measures means the Bosnian Serbs are willing to back down and peace may be at hand. A failure to enforce yet another Western ultimatum means more of the same in Bosnia.
* French pilots: Two French pilots are in Bosnian Serb hands. The quicker the French pilots are released, the more interested the Bosnian Serbs are in peace. The release of the pilots would also show how much control Milosevic, who quickly won the release of hundreds of UN hostages in June, truly has over his Bosnian Serb brethren.
* Body bags: The more pilots that are downed, the more Western resolve to challenge the Bosnian Serbs is likely to dissipate. Retaliatory Bosnian Serb shelling attacks on the mostly British and French peacekeepers on the ground in Sarajevo could weaken British and French support for airstrikes.
* Gorazde and Tuzla: The two UN ''safe areas'' in Bosnia with no Western camera crews in them could come under heavy Bosnian Serb attack. Without images of massacres flooding Western TV screens, US and European leaders could allow a Tuzla massacre or an attempt to take Gorazde slide.
* Bihac: The formerly besieged Muslim enclave in northwestern Bosnia liberated by the Croatian Army in early August has suddenly become the Bosnian Army's most powerful firebase. With resupply from neighboring Croatia now possible, the Bosnian Fifth Corps could launch a campaign to pressure or even take Banja Luka, the largest Serb-held city in Bosnia. A threat to take Banja Luka could pressure the Bosnian Serbs toward peace talks or harden their resolve to fight on, analysts say.
* Jacques Chirac: His recent election as French president, and his public calls for tougher action against the Serbs, have lessened the British-French opposition to heavy NATO airstrikes. But whether the right-wing Chirac will continue risking peacekeepers' lives in Sarajevo to push for a final settlement, versus a brief lull in the siege, is unclear.
* Rupert Smith: The British UN commander in Bosnia has quietly revolutionized the troubled peacekeeping mission. General Smith's pullback of peacekeepers from Serb-held territory eliminated the threat of Bosnian Serbs taking peacekeepers hostage in response to NATO airstrikes. If Smith's attempts at taking on the Bosnian Serbs, such as reopening a UN ''blue route'' into Sarajevo over the weekend without their permission, suddenly end - that may be a sign Western unity on pushing the Serbs is unraveling.
'What Americans better understand is that the American phase of this is just beginning.'
Aide to US senator