Sudan seeks presidency
Sudan has latterly sought to obtain the presidency of the AU, and the UN sources said they expected Bashir to be more open to persuasion if Khartoum secures the right to chair the organisation for the next 12 months.
However, some African states are strongly opposed to the possibility of Sudan assuming the chairmanship.
While the US has been critical of the Sudanese government, a senior official declined to give her verdict on the differences between African states on the chairmanship.
"It is good to have a debate. I hope the presidents can come to an early decision so that the other issues can also be addressed," said Jendayi Frazer, US assistant secretary of state for African affairs.
"It is up to the African leaders to decide," she said.
Ban and Bashir are expected to meet later in the day for what UN officials described as a "major showdown".
Ban is also expected to stress to the summit "the central importance" of a joint international effort to end the crisis in Darfur.
The UN estimates some 200,000 people have been killed since 2003 in the region.
Other issues expected to be discussed at the two day-summit include the deployment of peacekeepers to Somalia, global warming and Africa's first football World Cup.