EDITORIAL\Bosnian breakdowns\Incidents illustrate limits of coercion in trying to dictate peace.

IT was obvious from the start that the United States and its NATO allies had more than enough power to overwhelm the various combatants in Bosnia. And fortunately, none of those combatants has chosen so far to directly challenge the allies' enormous military supremacy.

But it also should have been obvious that NATO, despite all its military power, really cannot dictate a peace. It always is up to the parties themselves to make peace. That's the lesson of longtime U.S. diplomatic efforts to end Arab-Israeli hostilities, and it applies equally as well to the turmoil in Bosnia.

The futility of trying to dictate a peace was illustrated again Tuesday when Bosnian Serb leaders ordered Serbs in Sarajevo to leave neighborhoods being turned over to Bosnian Muslims. The evacuation order is consistent with the Bosnian Serb leader Radovan Karadzic's often-stated position that Serbs cannot coexist with Muslims and other ethnic groups in Bosnia's capital.

Meanwhile, efforts to encourage free movement between Muslim and Croat areas in Mostar broke down in a shouting match only hours after street barriers were removed.

The Mostar incident raises serious doubts about the viability of plans to establish a Muslim and Croat federation to govern half of Bosnia. Nevertheless, Secretary of State Warren Christopher, consistent with the rosy spin that the administration applies to every setback in Bosnia, insisted Tuesday that Mostar "is becoming a unified city."

Christopher also said Tuesday that President Clinton still plans to withdraw all U.S. troops from Bosnia by the end of the year. "If it were a longer period of time, it could be an excuse for the parties not to get into compliance (with the Dayton accords)," Christopher said.

But the various groups in Bosnia simply may be biding their time. They may be preparing to resume their warlike habits after American, British, French and other foreign forces leave.

That possibility gets to the heart of the problem with President Clinton's exercise in big-stick peacemaking. He risked U.S. prestige and American lives to achieve a peace that may not be in the cards in the absence of a strong desire for peaceful coexistence among the parties themselves.

The fact is that Clinton has left the United States with two options, neither of them pleasant, if the operation fails to achieve its lofty goals. One is to stay on - and run the risk of squandering more U.S. money, lives and credibility in Bosnia.

The other is to depart as planned, leaving Americans to wonder why the administration chose to risk U.S. lives on an objective it wasn't fully prepared to achieve in a conflict that didn't directly threaten U.S. interests.