THE surrender of the Muslim enclave of Zepa is the latest indication that rebel Serbs throughout the former Yugoslavia are mounting a successful, last-ditch military campaign that could allow them to dictate the terms of a future peace agreement.
Taking advantage of an overwhelming superiority in tanks and artillery that may soon disappear, the Serbs are forcing a summer military showdown in Bosnia on the best terms they can, Western analysts say. And they may be trying to force a United Nations pullout from Bosnia and Croatia.
Islamic states have said almost daily that they will break a UN arms embargo against the Muslim-led Bosnian government, while the US Congress is scheduled to vote on lifting the embargo July 26. Astute Serb leaders may feel now is their last chance to seize and ''ethnically cleanse'' vulnerable Muslim cities.
Meanwhile, Bosnian Serb leader Radovan Karazdic and army commander Gen. Ratko Mladic have been indicted for genocide and crimes against humanity by the Yugoslav War Crimes Tribunal in The Hague.
''There is some evidence that the Bosnian Serbs want to get this war over with,'' says a Western diplomat in Zagreb. ''Just grab all the territory that they can and call it a day.''
The rebel Serbs have some breathing time to continue this strategy. The new UN Rapid Reaction Force is not fully in place, American or Islamic heavy-weapons deliveries at least weeks away, and Western powers are divided over how many of the five remaining Muslim ''safe areas'' to protect with airstrikes. The ethnic cleansing of 75 percent of Bosnia could soon become a fait accompli, analysts say.
''There seems to be an endgame that they're playing,'' says Michael Williams, a former senior UN official in the Balkans and now a senior research fellow at the London-based International Institute for Strategic Studies. ''They let winter come and say okay, let's make a peace deal.''
UN forces on the ground reported July 25 that Bosnian Serb forces had entered Zepa, a city of 17,000 people, and that the Bosnian government Army was no longer in the city. The fall came two weeks to the day after Serbs seized another UN safe area, Srebrenica. The UN rushed a team of negotiators to Zepa, which Serb forces had attacked for days, to work out a surrender agreement.
The Serb military successes point to what critics say is a flaw in the American proposal to lift the UN arms embargo on Bosnia. The proposal by Senate majority leader Bob Dole (R) of Kansas allows a 12-week lapse between the time when the Bosnian government requests a UN withdrawal and when the US begins delivering weapons. The measure dodges the question of whether the US would provide airstrikes during that period to prevent more Serb marauding.
But the US effort to lift the embargo runs the risk of becoming an also-ran. Malaysia, Sudan, and wealthy Saudi Arabia have offered to ship weapons to Bosnia's Muslims or have called on other Islamic countries to send arms.
''With Islamic countries ignoring [the arms embargo], it would seem inevitable that the US might lift it,'' says a Zagreb-based diplomat. ''It would be quite hard for them to resist doing the same thing.''
For both rebel Serbs in Bosnia and Croatia, a military showdown makes sense for several reasons.
Rebel Serb forces in Bosnia have long been overstretched in trying to defend a front line that runs for more than 1,000 miles. They have reportedly been dogged by low morale and supplies. The Bosnian government Army has nearly twice as many troops as the Serbs and, if armed with heavy weapons, could quickly begin taking back territory.
''I remember [Bosnian Serb commander] Mladic saying in meetings that 'We can live with the diplomatic isolation,' '' says Mr. Williams, '' 'but we can see that in two years the [UN] economic sanctions will hurt us and the Bosnian government isn't short on backers.' ''
For the Serbs in Croatia, attacking the nearby ''safe area'' of Bihac may be a desperate attempt to deal with an impending military offensive from Croatia. Attacking Bihac invites action by Croatia and could draw powerful Serbia into the war.
''I think it's a highly dangerous tactic that will lead to Croatian intervention or NATO action,'' predicts Williams.
In a three-pronged attack that is seriously threatening the enclave of 200,000 people, Bosnian Serb forces are attacking Bihac from the east and southeast, Croatian Serb forces are attacking from the west, and rebel Muslims who oppose the government in Sarajevo are attacking from the northwest.
Bihac's residents have been worn down by Serb refusals to allow UN food convoys to enter the city. Last month, the first starvation deaths in a UN safe area were reported in Bihac.
Whether the Bosnian Serbs are trying to force all UN forces out of Bosnia remains unclear. But UN officials believe the Serbs will continue to take advantage of the fact that the West can't agree on whether to protect all safe areas or just Gorazde with severe airstrikes. ''By any logical behavior,'' Williams says, the Serbs will ''lay off Gorazde and go for broke in Bihac.''