The Taoiseach, Mr Ahern, was battling to reach a consensus among European Union leaders late last night after France expressed strong opposition to the appointment of Mr Chris Patten as successor to Commission President, Mr Romano Prodi.
The other strong contender, Mr Guy Verhofstadt, the Belgian Prime Minister, was effectively vetoed by Britain.
Faced with stalemate, Mr Ahern adjourned the meeting for an hour to conduct bilateral discussions on the appointment, which has left EU leaders seriously divided. Officials said that, with opinion so sharply divided, the decision on whom to appoint could be postponed until later this morning.
The two most prominent candidates last night were Mr Verhofstadt, who is backed by France and Germany, and the External Affairs Commissioner, Mr Patten, who yesterday won the support of the EU's centre-right European People's Party (EPP).
At the start of yesterday evening's session, which was conducted over a dinner of Wicklow lamb and asparagus, the Taoiseach told leaders that neither candidate had enough support to secure a qualified majority. The leaders agreed that, rather than put any candidate to a vote, Mr Ahern should hold individual consultations in an effort to find a consensus candidate.
Britain this week ruled out supporting Mr Verhofstadt and the French President, Mr Jacques Chirac, yesterday appeared to reject Mr Patten on the grounds that Britain is not in the euro-zone.
"It's difficult to have the representative of a country which doesn't take part in all European policies," he said.
Mr Chirac returned to France last night to attend a second World War commemoration today, leaving Germany's Mr Gerhard Schröder to negotiate on his behalf until he returns this afternoon.
The Taoiseach refused to be drawn on the subject of Mr Prodi's successor when he spoke to reporters before yesterday evening's dinner, saying only that it was important to find the right person for the job. "We need somebody dynamic who would be able to lead Europe in the next five years," he said.
Mr Ahern hinted, however, that Mr Patten's experience in external relations could be useful in a future Commission president.
"Europe on the international stage grows day by day, European involvement in so many regions of the world, we need somebody who can competently deal with that," Mr Ahern said.
Mr Patten is understood to have the support of up to half of the 25 member-states, including Italy, Austria, the Netherlands, Portugal, Slovenia, Malta and Estonia. The opposition of France and Germany could, however, prove an insuperable barrier to his appointment.
For his part, Mr Verhofstadt faces opposition from Britain, Italy, Latvia, Lithuania, Poland and the Czech Republic.
Irish presidency officials said last night that, if opposition to Mr Verhofstadt and Mr Patten did not diminish, Mr Ahern would seek to establish the level of support for compromise candidates.
The most popular alternative would almost certainly be Luxembourg's Mr Jean-Claude Juncker but Mr Juncker has stated emphatically that he intends to remain in the Grand Duchy for a further five years. A number of leaders would like the Taoiseach to take on the position himself but Mr Ahern insists that he is not a candidate.
The impasse over Mr Prodi's successor followed a discussion yesterday afternoon of the constitutional treaty, during which most leaders welcomed the Irish Presidency's latest proposals.
The Taoiseach said he believed the leaders were "closing in" on an agreement but warned that a number of issues remain to be resolved.
"I am not over-optimistic. There are still many difficult issues to be resolved," he said.
Diplomats were confident last night that a deal on the constitution would be reached today, although Mr Chirac warned that Britain's insistence on retaining the national veto in a number of policy areas was hampering progress.