SARAJEVO, Bosnia-Herzegovina (AP) _ Bosnian Croats backed out of an agreement to turn Sarajevo over to a Croat-Muslim government Monday, reflecting the mistrust that threatens the fragile Bosnian peace accord.

The Croat-Muslim federation was formed under U.S. pressure in March 1994 after the two ethnic groups engaged in a nearly year-long war. But lingering enmity has kept it weak and hobbled its effectiveness as a counterweight to the Bosnian Serb republic that makes up the other half of Bosnia.

The Croat-Muslim agreement to jointly govern Sarajevo and its suburbs was signed a month ago by Kresimir Zubak, the Croat president of the federation, and Ejup Ganic, its Muslim vice president.

The Bosnian Croats gave no explanation for backing out Monday, but federation sources said the Croats feared they would be outvoted by the Muslims in such a framework.

Muslim-Croat cooperation in Sarajevo is considered essential to the broader peace plan for Bosnia, because Muslims and Croats are supposed to work closely in governing half the country.

A senior Bosnian Croat leader, Ante Zelic, said Monday that Sarajevo could turn into an even bigger problem than the southwestern city of Mostar. Distrust between Croats and Muslims hobbled efforts to reunite the bitterly divided city.

Croats rioted last month against a European Union decision to draw city boundaries with a neutral central district, forcing the EU administrator, Hans Koschnick, to resign.

Also Monday, Bosnian Serb leaders appealed to Belgrade for help in evacuating thousands of Bosnian Serbs from districts the Serbs must hand over to the Muslim-Croat federation by March 19.

Bosnian Serb leaders wrote to Serbian President Slobodan Milosevic asking for help in getting thousands of Serbs out of three districts they still hold in Sarajevo before police from the Muslim-Croat federation take full control.

Milosevic negotiated the peace accord on behalf of Bosnia's Serbs, who have raged at their former patron for giving away one of their biggest prizes _ Serb Sarajevo.

Many of the estimated 70,000 residents of Serb areas of Sarajevo have fled since the accord was announced, with the exodus gaining momentum in the past two weeks.

The international police force overseeing the transfer said it has received daily reports of Serbs who fled Sarajevo forcing Muslims and Croats from their homes in Serb-held Bosnia. About 160 incidents are known so far, said Alexander Ivanko, spokesman for the U.N. police force.

On the other hand, U.N. officials have also received some reports of intimidation of Serbs who remained in suburbs already turned over to Croat-Muslim control.

More than 200 Muslims driven out of the village of Nahorevo, 4 1/2 miles north of Sarajevo, returned Monday to the homes they fled in 1992.

They came back through a still uncleared minefield, walking two by two in silence in each other's tracks to avoid being blown up.

Nahorevo's clinic was burned down Sunday as the last Serbs departed. Only a handful of Serbs remained Monday, including a pensioner who worked as a nurse at the clinic for 25 years.

``I have decided to stay because I don't have anywhere else to go,'' said Mira Ninkovic, 68.

She said she thought she had nothing to fear, and tried to persuade others to stay, but ``they were convinced the Muslims will beat them and mistreat them.''