As the chief U.N. war crimes prosecutor, Carla Del Ponte briefed U.S. and European diplomats at the Swiss ambassador's residence in Belgrade last month on her latest efforts to capture Balkan war criminals, a wanted former Bosnian Serb general, Ratko Mladic, sat down at a nearby restaurant and dined with friends, according to sources close to the prosecutor.

Del Ponte was not aware on that Oct. 21 evening that just blocks away at the Konak restaurant in Belgrade's Topcidersko Brdo neighborhood, one of the Balkans' most notorious war crimes suspects was publicly flouting demands that he surrender to the war crimes court in the Hague. It was not the first time. Mladic's whereabouts in Belgrade have become an open secret and the Yugoslav authorities have either been unwilling or unable to capture him, Del Ponte said.

U.N. Secretary General Kofi Annan is planning to visit Belgrade Tuesday to press President Vojislav Kostunica of the Federal Republic of Yugoslavia, which is comprised of the republics of Serbia and Montenegro, to hand over Mladic. Del Ponte, who is scheduled to meet in Belgrade with Annan on Wednesday, said that her own efforts to persuade the government to cooperate have been unsuccessful, despite regular intelligence reports on Mladic's movements over the past year.

Mladic is charged with ordering the murder of thousands of civilians in the Bosnian Muslim village of Srebrenica in July 1995, the largest mass killing in Europe since World War II. Despite the arrest of Yugoslav President Slobodan Milosevic by Serbian police in April 2001, Mladic and several other Balkans war crimes suspects remain at large.

Milosevic was transferred to the Hague for trial in June 2001.

The defiance of the United Nations by Yugoslavia has proven awkward for the Bush administration, which threatened to cut off aid last year to pressure Belgrade to arrest Milosevic. It illustrates how what was once a key U.S. foreign policy goal -- prosecuting those responsible for atrocities in the Balkans -- has been sidelined by the war on terrorism and the effort to disarm Iraq.

Mladic has slept at the home of a former Yugoslav general and visited the main military hospital in Belgrade at least twice this year, according to Del Ponte.

Prime Minister Zoran Djinjic of the Yugoslav republic of Serbia, which has been more sympathetic to Del Ponte's appeals, and other Serbian officials have privately acknowledged that Mladic is living in Belgrade under the protection of the Yugoslav military. "I have good information" about Mladic's activities," Del Ponte said. "And the authorities in Belgrade didn't deny it. They know. They are telling me, 'we can do nothing because we cannot risk . . . an armed conflict [between] the army and the police.' "

Yugoslavia's U.N. ambassador, Dejan Sahovic, is in Belgrade for Annan's visit and unavailable for comment on Mladic's movements, according to an official in his office. But he told the U.N. Security Council last month that Yugoslavia's cooperation with the court "has been constantly improving." He said that the government had responded to 34 requests from the Hague for documents and that as many as 14 indictees, including Milosevic, had been transferred to the court.

An unidentified man reached by telephone at the Konak restaurant denied that Mladic had visited the restaurant last month, but suggested that he may have been a former customer, saying we "haven't seen him for two years."

Senior U.S. officials acknowledge that they have turned down the heat in recent months, but only because they feared that American pressure would benefit nationalist candidates in this year's Bosnian and Yugoslav elections.

"In the past couple of months everyone has been in a holding pattern while we have been watching the electoral process play out both in Bosnia and Yugoslavia," said a senior administration official. "We haven't forgotten. I think you can expect to see us getting aggressive on this issue once the election season ends."

Despite U.S. efforts, there are few indications that Serb authorities in Bosnia and Yugoslavia are feeling the pressure. Milan Milutinovic, a senior Serbian official who was indicted in May 1999 for his role in the expulsion of ethnic Albanians from Kosovo, remains president of Serbia.

Former Bosnian Serb president Radovan Karadzic, Mladic's main political ally during the 1992-1995 Bosnian war, has avoided thousands of NATO forces in the Bosnian Serb-controlled province of the Serb Republic. Forces of the NATO-led Stabilization Force have failed to capture him despite several attempts.

Staff writer Dan Morgan in Washington contributed to this report.