SARAJEVO-Bosnia-Herzegovina (AP) _ Heading to a crucial summit on the Bosnian peace plan, a top U.S. envoy said Saturday he was seeking a guarantee that Bosnian Serb leader Radovan Karadzic was out of power.

Sources close to Karadzic, who has been accused of war crimes, said Serbian President Slobodan Milosevic would present a document showing Karadzic's effective removal when he meets in Geneva on Sunday with U.S. Secretary of State Warren Christopher and the presidents of Bosnia and Croatia.

Karadzic's ouster, a requirement of the Bosnia peace agreement, has been a key demand of the United States and Western allies who sent NATO-led foreign troops to Bosnia to implement the peace plan.

In a possible sign that moves were afoot to sideline Karadzic, at least formally, the Yugoslav news agency Tanjug reported that Biljana Plavsic, Karadzic's designated deputy, would attend the Geneva meeting.

Belgrade's independent Beta news agency reported Karadzic agreed to sign a letter of resignation. The report could not be confirmed.

Assistant U.S. Secretary of State John Kornblum told a news conference he was unaware of any plans for Milosevic to announce his former protege's resignation. He described a fiery meeting with Milosevic on Friday that produced little agreement.

``I didn't have any indication of this from Mr. Milosevic yesterday,'' Kornblum said. ``The proof will come in the doing. The proof will come if Karadzic is clearly not in the vicinity of power.''

Karadzic and his senior military commander, Gen. Ratko Mladic, have been indicted by a U.N. war crimes tribunal for alleged atrocities during the 43-month Bosnian war.

Their removal, and the arrest of dozens of other indicted war criminals, is a key provision of the peace agreement signed by Milosevic in the name of Bosnia's rebel Serbs.

Last month Karadzic handed much of his duties to Plavsic. But she is considered an even more hard-line nationalist and the international community has shunned her.

Before departing for Geneva, however, she made conciliatory comments and conspicuously avoided mentioning Karadzic's name at all, Tanjug reported.

Kornblum noted Saturday a statement from Plavsic pledging full cooperation with Dayton's provisions, which he called a positive step.

The U.S. envoy said he told Milosevic that Serb-led Yugoslavia would face renewed economic sanctions unless the accord was upheld. In addition, the United States would block international financial institutions from working with Yugoslavia.

Milosevic had replied that ``he would continue his policies and he believed that he was fully implementing Dayton,'' said Kornblum. ``In other words, we didn't obviously reach any agreement on this.''

``I said very clearly to him that the possibility of sanctions was there, it was probably growing greater,'' he said.

The peace accord, signed late last year, splits Bosnia into a Muslim-Croat federation that holds 51 percent of the country and a Bosnian Serb entity controlling 49 percent, with a loose, joint leadership overseeing them.

Sunday's Geneva summit is intended to set a date for elections this fall and to clarify Karadzic's fate.