The sources said the Security Council was expected to adopt a full resolution, giving its blessing to the peace agreement and to the Nato force, which is gathering on Kosovo's borders.
The resolution will approve the setting up of a massive UN-controlled civilian mission, charged with running the devastated province. The resolution could be adopted as early as today, the sources said.
"It will be a UN operation on the civilian side, a military operation with Nato at its core and blessed by a Security Council resolution," said Shashi Tharoor, spokesman for Kofi Annan, UN secretary-general. "The war was a Nato war, the peace will be a United Nations peace."
The breakthrough came after members of the Yugoslav army delegation, who had left the talks for consultations with Belgrade, turned around in mid-journey and returned to the talks with the Nato commander, General Sir Michael Jackson.
The U-turn followed an agreement on amendments to the military accord, making it more palatable to the Yugoslav side. At the same time, Yugoslavia's ambassador in New York was instructed to approve the agreement, lifting the threat of a Security Council veto from China, angry at the air campaign and still furious over Nato's bombing of its Belgrade embassy.
The meeting this week of the Group of Eight foreign ministers of the leading powers, in Cologne, paved the way for last night's agreement. British officials said it did not affect the wording of the draft UN resolution, but was simply a "clarification" of the timetable for the start of a Serb withdrawal, a halt in the bombing and passage of the resolution in the Security Council.
The Foreign Secretary, Robin Cook, said the clarification met the last doubts of the Serbs. There was no question of an end to the bombing before Serb forces started to withdraw from Kosovo, he said.
The German Foreign Minister, Joschka Fischer, said Nato was now willing to drop a sentence in the proposed withdrawal agreement that provided for a 24-hour delay between the Yugoslav pullout and the arrival of international peace-keepers.
This was a key sticking point for the Yugoslavs, who fear Kosovo Liberation Army fighters will exploit that delay to rush their troops and weapons into the province and wreak havoc on the retreating Serbian forces.
If the resolution is adopted, some British and American forces could be in Kosovo within days to verify the departure of Serb troops. The bombing will then cease, paving the way for the 50,000 peace-keepers to supervise the refugees' return.